There isn't a way to change icon color that I know of. Why don't you just seperate sms and be done with it? You can also edit a profile to give different sounds, etc for e-mails and sms so you can tell what's what when you receive them if you want to leave them combined. Here's a link on how to do that...
I had my icons different by downloading a theme builder and keep everything the same except the icons I wanted different. Example I colored each one of my e-mail icons (8 of them) so I could fast reference.
