<s>
A	O
color	O
tool	O
or	O
other	O
graphics	B-Application
software	I-Application
is	O
often	O
used	O
to	O
generate	O
color	O
values	O
.	O
</s>
<s>
Colors	O
outside	O
the	O
sRGB	O
gamut	O
can	O
be	O
specified	O
in	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
by	O
making	O
one	O
or	O
more	O
of	O
the	O
red	O
,	O
green	O
and	O
blue	O
components	O
negative	O
or	O
greater	O
than	O
100%	O
,	O
so	O
the	O
color	O
space	O
is	O
theoretically	O
an	O
unbounded	O
extrapolation	O
of	O
sRGB	O
similar	O
to	O
scRGB	B-Device
.	O
</s>
<s>
It	O
is	O
impossible	O
with	O
the	O
hexadecimal	O
syntax	O
(	O
and	O
thus	O
impossible	O
in	O
legacy	O
HTML	B-Language
documents	O
that	O
do	O
not	O
use	O
CSS	B-Language
)	O
.	O
</s>
<s>
The	O
first	O
versions	O
of	O
Mosaic	B-Application
and	O
Netscape	B-Protocol
Navigator	I-Protocol
used	O
the	O
X11	B-Device
color	I-Device
names	I-Device
as	O
the	O
basis	O
for	O
their	O
color	O
lists	O
,	O
as	O
both	O
started	O
as	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
applications	O
.	O
</s>
<s>
These	O
have	O
been	O
chosen	O
to	O
be	O
similar	O
to	O
many	O
real-world	O
monitors	B-Device
and	O
viewing	O
conditions	O
,	O
to	O
allow	O
rendering	O
to	O
be	O
fairly	O
close	O
to	O
the	O
specified	O
values	O
even	O
without	O
color	O
management	O
.	O
</s>
<s>
User	B-Protocol
agents	I-Protocol
vary	O
in	O
the	O
fidelity	O
with	O
which	O
they	O
represent	O
the	O
specified	O
colors	O
.	O
</s>
<s>
More	O
advanced	O
user	B-Protocol
agents	I-Protocol
use	O
color	O
management	O
to	O
provide	O
better	O
color	O
fidelity	O
;	O
this	O
is	O
particularly	O
important	O
for	O
Web-to-print	O
applications	O
.	O
</s>
<s>
A	O
hex	O
triplet	O
is	O
a	O
six-digit	O
,	O
three-byte	O
hexadecimal	O
number	O
used	O
in	O
HTML	B-Language
,	O
CSS	B-Language
,	O
SVG	B-Application
,	O
and	O
other	O
computing	O
applications	O
to	O
represent	O
colors	O
.	O
</s>
<s>
The	O
bytes	B-Application
represent	O
the	O
red	O
,	O
green	O
,	O
and	O
blue	O
components	O
of	O
the	O
color	O
.	O
</s>
<s>
One	O
byte	B-Application
represents	O
a	O
number	O
in	O
the	O
range	O
00	O
to	O
FF	O
(	O
in	O
hexadecimal	O
notation	O
)	O
,	O
or	O
0	O
to	O
255	O
in	O
decimal	O
notation	O
.	O
</s>
<s>
The	O
hex	O
triplet	O
is	O
formed	O
by	O
concatenating	O
three	O
bytes	B-Application
in	O
hexadecimal	O
notation	O
,	O
in	O
the	O
following	O
order	O
:	O
</s>
<s>
Expanding	O
this	O
form	O
to	O
the	O
six-digit	O
form	O
is	O
as	O
simple	O
as	O
repeating	O
each	O
digit	O
:	O
09C	O
becomes	O
0099CC	O
as	O
presented	O
on	O
the	O
following	O
CSS	B-Language
example	O
:	O
</s>
<s>
Conversion	O
between	O
number	O
bases	O
is	O
a	O
common	O
feature	O
of	O
calculators	O
,	O
including	O
both	O
hand-held	O
models	O
and	O
the	O
software	O
calculators	O
bundled	O
with	O
most	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
In	O
HTML	B-Language
and	O
XHTML	O
,	O
colors	O
can	O
be	O
used	O
for	O
text	O
,	O
background	O
color	O
,	O
frame	O
borders	O
,	O
tables	O
,	O
and	O
individual	O
table	O
cells	O
.	O
</s>
<s>
The	O
basic	O
colors	O
are	O
16	O
colors	O
defined	O
in	O
the	O
HTML	B-Language
4.01	I-Language
specification	O
,	O
ratified	O
in	O
1999	O
,	O
as	O
follows	O
(	O
names	O
are	O
defined	O
in	O
this	O
context	O
to	O
be	O
case-insensitive	O
)	O
:	O
</s>
<s>
These	O
16	O
were	O
labelled	O
as	O
sRGB	O
and	O
included	O
in	O
the	O
HTML	B-Language
3.0	O
specification	O
,	O
which	O
noted	O
they	O
were	O
"	O
the	O
standard	O
16	O
colors	O
supported	O
with	O
the	O
Windows	O
VGA	B-Protocol
palette.	O
"	O
</s>
<s>
Extended	O
colors	O
are	O
the	O
result	O
of	O
merging	O
specifications	O
from	O
HTML	B-Language
4.01	I-Language
,	O
CSS	B-Language
2.0	I-Language
,	O
SVG	B-Application
1.0	I-Application
and	O
CSS3	O
User	O
Interfaces	O
(	O
CSS3	O
UI	O
)	O
.	O
</s>
<s>
Several	O
colors	O
are	O
defined	O
by	O
web	B-Application
browsers	I-Application
.	O
</s>
<s>
A	O
particular	O
browser	B-Application
may	O
not	O
recognize	O
all	O
of	O
these	O
colors	O
,	O
but	O
as	O
of	O
2005	O
,	O
all	O
modern	O
,	O
general-use	O
,	O
graphical	O
browsers	B-Application
support	O
the	O
full	O
list	O
of	O
colors	O
.	O
</s>
<s>
Many	O
of	O
these	O
colors	O
are	O
from	O
the	O
list	O
of	O
X11	B-Device
color	I-Device
names	I-Device
distributed	O
with	O
the	O
X	B-Operating_System
Window	I-Operating_System
System	I-Operating_System
.	O
</s>
<s>
These	O
colors	O
were	O
standardized	O
by	O
SVG	B-Application
1.0	I-Application
,	O
and	O
are	O
accepted	O
by	O
SVG	B-Application
Full	I-Application
user	B-Protocol
agents	I-Protocol
.	O
</s>
<s>
They	O
are	O
not	O
part	O
of	O
SVG	B-Application
Tiny	I-Application
.	O
</s>
<s>
The	O
list	O
of	O
colors	O
shipped	O
with	O
the	O
X11	B-Operating_System
product	O
varies	O
between	O
implementations	O
and	O
clashes	B-Application
with	O
certain	O
of	O
the	O
HTML	B-Language
names	O
such	O
as	O
green	O
.	O
</s>
<s>
X11	B-Device
colors	I-Device
are	O
defined	O
as	O
simple	O
RGB	O
(	O
hence	O
,	O
no	O
particular	O
color	O
space	O
)	O
,	O
rather	O
than	O
sRGB	O
.	O
</s>
<s>
This	O
means	O
that	O
the	O
list	O
of	O
colors	O
found	O
in	O
X11	B-Operating_System
(	O
e.g.	O
,	O
in	O
/usr/lib/X11/rgb.txt	O
)	O
should	O
not	O
directly	O
be	O
used	O
to	O
choose	O
colors	O
for	O
the	O
web	O
.	O
</s>
<s>
The	O
list	O
of	O
web	O
"	O
X11	B-Device
colors	I-Device
"	O
from	O
the	O
CSS3	O
specification	O
,	O
along	O
with	O
their	O
hexadecimal	O
and	O
decimal	O
equivalents	O
,	O
is	O
shown	O
below	O
.	O
</s>
<s>
This	O
includes	O
the	O
common	O
synonyms	O
:	O
aqua	O
(	O
HTML4/CSS	O
1.0	O
standard	O
name	O
)	O
and	O
cyan	O
(	O
common	O
sRGB	O
name	O
)	O
,	O
fuchsia	O
(	O
HTML4/CSS	O
1.0	O
standard	O
name	O
)	O
and	O
magenta	B-Algorithm
(	O
common	O
sRGB	O
name	O
)	O
,	O
gray	O
(	O
HTML4/CSS	O
1.0	O
standard	O
name	O
)	O
and	O
grey	O
.	O
</s>
<s>
The	O
Cascading	B-Language
Style	I-Language
Sheets	I-Language
specification	O
defines	O
the	O
same	O
number	O
of	O
named	O
colors	O
as	O
the	O
HTML	B-Language
4	O
spec	O
,	O
namely	O
the	O
16	O
html	B-Language
colors	O
,	O
and	O
124	O
colors	O
from	O
the	O
Netscape	O
X11	B-Device
color	I-Device
list	O
for	O
a	O
total	O
of	O
140	O
names	O
that	O
were	O
recognized	O
by	O
Internet	O
Explorer	O
(	O
IE	O
)	O
3.0	O
and	O
Netscape	B-Protocol
Navigator	I-Protocol
3.0	O
.	O
</s>
<s>
In	O
CSS	B-Language
2.1	I-Language
,	O
the	O
color	O
'	O
orange	O
 '	O
(	O
one	O
of	O
the	O
140	O
)	O
was	O
added	O
to	O
the	O
section	O
with	O
the	O
16	O
HTML4	O
colors	O
as	O
a	O
17th	O
color	O
.	O
</s>
<s>
In	O
the	O
same	O
reference	O
,	O
the	O
"	O
SVG	B-Application
color	O
keywords	O
"	O
section	O
,	O
was	O
renamed	O
"	O
Extended	O
color	O
keywords	O
"	O
,	O
after	O
starting	O
out	O
as	O
"	O
X11	B-Device
color	I-Device
keywords	O
"	O
in	O
an	O
earlier	O
working	O
draft	O
.	O
</s>
<s>
CSS	B-Language
2	I-Language
,	O
SVG	B-Application
and	O
CSS	B-Language
2.1	I-Language
allow	O
web	O
authors	O
to	O
use	O
system	O
colors	O
,	O
which	O
are	O
color	O
names	O
whose	O
values	O
are	O
taken	O
from	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
picking	O
the	O
operating	B-General_Concept
system	I-General_Concept
's	O
highlighted	O
text	O
color	O
,	O
or	O
the	O
background	O
color	O
for	O
tooltip	O
controls	O
.	O
</s>
<s>
This	O
enables	O
web	O
authors	O
to	O
style	O
their	O
content	O
in	O
line	O
with	O
the	O
operating	B-General_Concept
system	I-General_Concept
of	O
the	O
user	B-Protocol
agent	I-Protocol
.	O
</s>
<s>
The	O
CSS3	O
color	O
module	O
has	O
deprecated	B-General_Concept
the	O
use	O
of	O
system	O
colors	O
in	O
favor	O
of	O
CSS3	O
UI	O
System	O
Appearance	O
property	O
,	O
which	O
itself	O
was	O
subsequently	O
dropped	O
from	O
CSS3	O
.	O
</s>
<s>
CSS	B-Language
also	O
supports	O
the	O
special	O
color	O
transparent	O
,	O
which	O
represents	O
an	O
alpha	O
value	O
of	O
zero	O
;	O
by	O
default	O
,	O
transparent	O
is	O
rendered	O
as	O
an	O
invisible	O
nominal	O
black	O
:	O
rgba(0, 0, 0, 0 )	O
.	O
</s>
<s>
It	O
was	O
introduced	O
in	O
CSS1	B-Language
but	O
its	O
scope	O
of	O
use	O
has	O
expanded	O
over	O
the	O
versions	O
.	O
</s>
<s>
Level	O
4	O
of	O
the	O
CSS	B-Language
Color	O
specification	O
introduced	O
several	O
new	O
CSS	B-Language
color	O
formats	O
.	O
</s>
<s>
CSS	B-Language
Color	O
4	O
introduces	O
several	O
different	O
formats	O
for	O
device	O
independent	O
color	O
that	O
can	O
display	O
the	O
entirety	O
of	O
visible	O
color	O
(	O
in	O
a	O
capable	O
screen	O
)	O
,	O
including	O
:	O
</s>
<s>
On	O
21	O
June	O
2014	O
,	O
the	O
CSS	B-Language
WG	O
added	O
the	O
color	O
RebeccaPurple	O
to	O
the	O
Editor	O
's	O
Draft	O
of	O
the	O
Colors	O
module	O
level	O
4	O
,	O
to	O
commemorate	O
Eric	O
Meyer	O
's	O
daughter	O
Rebecca	O
,	O
who	O
died	O
on	O
7	O
June	O
2014	O
,	O
her	O
sixth	O
birthday	O
.	O
</s>
<s>
The	O
draft	O
CSS	B-Language
Color	O
5	O
specification	O
introduces	O
syntax	O
for	O
mixing	O
and	O
manipulating	O
existing	O
colors	O
,	O
including	O
:	O
</s>
<s>
A	O
set	O
of	O
colors	O
was	O
needed	O
that	O
could	O
be	O
shown	O
without	O
dithering	O
on	O
256-color	O
displays	O
;	O
the	O
number	O
216	O
was	O
chosen	O
partly	O
because	O
computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
customarily	O
reserved	O
sixteen	O
to	O
twenty	O
colors	O
for	O
their	O
own	O
use	O
;	O
it	O
was	O
also	O
selected	O
because	O
it	O
allows	O
exactly	O
six	O
equally	O
spaced	O
shades	O
of	O
red	O
,	O
green	O
,	O
and	O
blue	O
(	O
6	O
×	O
6	O
×	O
6	O
=	O
216	O
)	O
,	O
each	O
from	O
00	O
to	O
FF	O
(	O
including	O
both	O
limits	O
)	O
.	O
</s>
<s>
These	O
colors	O
were	O
chosen	O
specifically	O
because	O
they	O
matched	O
the	O
palettes	O
selected	O
by	O
various	O
browser	B-Application
applications	O
.	O
</s>
<s>
There	O
were	O
not	O
very	O
different	O
palettes	O
in	O
use	O
in	O
different	O
browsers	B-Application
.	O
</s>
<s>
"	O
Web-safe	O
"	O
colors	O
had	O
a	O
flaw	O
in	O
that	O
,	O
on	O
systems	O
such	O
as	O
X11	B-Operating_System
where	O
the	O
palette	O
is	O
shared	O
between	O
applications	O
,	O
smaller	O
color	O
cubes	O
(	O
5×5×5	O
or	O
4×4×4	O
)	O
were	O
allocated	O
by	O
browsers	B-Application
—	O
the	O
"	O
web-safe	O
"	O
colors	O
would	O
dither	O
on	O
such	O
systems	O
.	O
</s>
<s>
Different	O
results	O
were	O
obtained	O
by	O
providing	O
an	O
image	O
with	O
a	O
larger	O
range	O
of	O
colors	O
and	O
allowing	O
the	O
browser	B-Application
to	O
quantize	B-Algorithm
the	O
color	O
space	O
if	O
needed	O
,	O
rather	O
than	O
suffer	O
the	O
quality	O
loss	O
of	O
a	O
double	O
quantization	O
.	O
</s>
<s>
David	O
Lehn	O
and	O
Hadley	O
Stern	O
discovered	O
that	O
only	O
22	O
of	O
the	O
216	O
colors	O
in	O
the	O
web-safe	O
palette	O
are	O
reliably	O
displayed	O
without	O
inconsistent	O
remapping	O
on	O
16-bit	O
computer	B-Device
displays	I-Device
.	O
</s>
<s>
Some	O
browsers	B-Application
and	O
devices	O
do	O
not	O
support	O
colors	O
.	O
</s>
<s>
Either	O
no	O
colors	O
should	O
be	O
specified	O
(	O
to	O
invoke	O
the	O
browser	B-Application
's	O
default	O
colors	O
)	O
,	O
or	O
both	O
the	O
background	O
and	O
all	O
foreground	O
colors	O
(	O
such	O
as	O
the	O
colors	O
of	O
plain	O
text	O
,	O
unvisited	O
links	O
,	O
hovered	O
links	O
,	O
active	O
links	O
,	O
and	O
visited	O
links	O
)	O
should	O
be	O
specified	O
to	O
avoid	O
black	O
on	O
black	O
or	O
white	O
on	O
white	O
effects	O
.	O
</s>
<s>
Among	O
their	O
other	O
color	O
pairs	O
,	O
brown	O
(	O
#282800	O
)	O
on	O
dark	O
green	O
(	O
#A0A000	O
)	O
has	O
a	O
contrast	O
ratio	O
of	O
3.24:1	O
,	O
which	O
is	O
less	O
than	O
the	O
WCAG	O
recommendation	O
,	O
dark	O
brown	O
(	O
#1E1E00	O
)	O
on	O
light	B-Device
green	I-Device
(	O
#B9B900	O
)	O
has	O
a	O
contrast	O
ratio	O
of	O
4.54:1	O
and	O
blue	O
(	O
#00007D	O
)	O
on	O
yellow	O
(	O
#FFFF00	O
)	O
has	O
a	O
contrast	O
ratio	O
of	O
11.4:1	O
.	O
</s>
