you can install trackball alert for free from the market. and when you do the test notification the color will change. but for some reason the actual notifications are not working yet with trackball alert on froyo unless you are rooted. i think trackball alert will be updated to fix.
you can also install handcent which has the setting for your texts to be any color you want. that will work no problem. and other apps like sms count can change your gmail color, etc.
blink is another free app in the market, this one DOES work with standard froyo, but it only lets you configure a couple apps, not quite as many as trackball alert. but its good enough for you to at least get the colors working