I was able to come up with a shitty hack:
I switched
Lua Code:
chatMessage = string.format('|cff'..RGBPercToHex(info.r, info.g, info.b)..'%s|r', chatMessage)
to
Lua Code:
chatMessage = gsub(string.format('|cff'..RGBPercToHex(info.r, info.g, info.b)..'%s', chatMessage), '|h|r', '|h|r|cff'..RGBPercToHex(info.r, info.g, info.b))
which basically just looks for the return signature used by achievements, items, etc and replaces it with a hex open of our chat channel color