In the WotLK client, you need to change colors in (at least) two places in Wow.exe. One for chat links, one for tooltips.
Search for the hex color code in IDA and you'll find the one used for chat links at this address:
00A24644
Keep in mind it's stored as a string (
https://www.asciitohex.com/)
For the other place, I looked around for GetItemQualityColor and found something pointing to:
0AD2D84
Keep in mind these are just stored as hex directly AND they're stored as BGR from top to bottom, rather than RGB.
Apologies if I fucked something up.
Am I correct in understanding that to safely add more color codes, you would change offsets to the end of the file where there's plenty of space?