I would like to change the text you type your username and password in with on the Lion login screen. I have a Command and conquer login screen and I would like to change the colour of the username and password Green and change the font. Is this Possible and how would i do it ?
Apple's ideology is mostly to not let the user tweak the design because, in many cases, the user may choose inferior fonts, colors, etc, and thus make Apple production look bad.
Instead of forcing design choices on user, as proudly does Linux and often does Windows, OS X contains settings that Apple considers “best” for everyone.
Of course, some people complain about certain decisions but it's much like MySpace vs Facebook. You can't change fonts and colors on a Facebook page, but frankly, imagine what a mess it would be if anyone could.
Presumably for this reasons, you can't customize how the text looks in input fields, including the login screen.