When you say that the color data consists of values from 0 to 255, do you mean that you have red, green and blue values for each point? In that case you can use glColor3b(red[i][j],green[i][j],blue[i][j]); (if your color arrays are called red,green and blue). I'm actually not sure how to do non-RGB colours in OpenGL so I don't think I can help you if my assumption is incorrect.
No I don't have RGB for each point. I am tring to use the last array as my texture for the 3D point cloud. But first I need to generate the point cloud. That' where I am stuck at. How would I go about generating the point cloud (creat a mesh or a surface????) using the 3 array I have. That's the main question.