Exactly, what does this represent?
Example:
If a player shows Red 60 and blue up to 95, does that mean he is at 95, or is it his potential to get to 95?

Current and Potential. Both could go up or down as time passes.

95 would be the potential.

What WarEagle said. The color of the rating is only to easily see how high it is. The bluer it is, the higher the rating. 90 will always be a much brighter blue than 50. The lower, the redder.

If you get lucky, a players max rating can sometimes grow as well, usually in the right system

Oh...so it changes from game to game? It doesn't stay the same once it's established?

Usually over the course of the season and ultimately career

thank you.....

Here's a really good blog post by jdavid:
http://blog.myfootballnow.com/2014/06/creepers-and-busts-dont-throw-away-your.html

It explains a bit more into detail about how players' overalls progress over the season and careers. Might be more helpful to you if you are still confused.