After thinking about it, I realized that my question was somewhat ambiguios, but I am gonna assume you knew what I was thinking (in a non-psychic kind of way
).
In the EQUI_HotButtonWnd.xml file, you would find the button that you want the color to be different. For example, I want to change the 6th button on the first hotbutton pad. I would look for the element labeled HB_Button6 (this is the default naming). In that element, you would find a set of tags that look like:
<TextColor>
<R>255</R>
<G>255</G>
<B>255</B>
</TextColor>
Set the RGB values to whatever color you want. Note: It will be this color for whatever hotkey you put there, with the exception of social hotkeys. They can define their colors in game.
If that is what you already have tried, then I would have to see your whole hotbutton file to see if I can track down the problems.