Hi. While I can't help you with the font color, because I've never done that, I can, however, help with the background color of your text and the bubble colors.
Now, please realize that I have an iPhone 4S - so I hope that the names and file locations are the same. I apologize in advance if they are not. Also, I will only be able to tell you the sizes and such of the wallpaper that I have on my phone, you may have to modify it to fit on your phone. Oh, and this is with iOS 5.0.1.
With all the qualifiers out of the way, I'm going to assume you don't already have a theme. So, you need to make one:
1) Create a folder on your computer and title it whatever you want, but have it ending in .theme (i.e. Example.theme)
2) Place two PNG images in there (this will be for your text background) and have them named
SMSBackground.png (480x480 size)
SMSBackground@2x.png (960x960; though I think this would be for retina devices)
Remember that all file names are case sensitive (apple is not the same as Apple)
3) Inside your Example.theme folder, make another folder titled Bundles. Then, make another folder inside that titled com.apple.chatkit. Your path will then look like this: Example.theme > Bundles > com.apple.chatkit
4) You will put your chat bubbles inside this folder (again, these are for iOS 5). If you don't want to make simple blocks of color, you can do a search of the Internet to find bubbles to modify. The key is that you want them named:
Balloon_2@2x.png (the gray bubble for received messages)
Balloon_1@2x.png (the green bubble for outgoing message)
Balloon_Blue@2x.png (the blue bubble for iMessages)
NOTE: If you just want to modify the existing bubble, go to this location on your phone (/System/Library/PrivateFrameworks/Chatkit.framework) and copy those three PNG images for modding on your computer. Then you can keep the same files, but just change the color...
5) Now that you have the theme folder made, put it on your phone (I use iFunbix cause it's easiest). It goes in this location:
/var/stash/Themes/
6) Once the theme is on your phone, go to Winterboard via your Settings app, select it, respring and you should be good to go.
You can also add these images to an existing theme should you wish to not make a separate one.
Hope this helps. Holler if you have questions.
Marilyn
