They're the same, the color coding is for you to be able to segregate them for different uses, if you wanted to do that (the point being that you might want to launder your towels differently if they have different contaminants, or your might want to separate towels that you use for paint from towels you use for less sensitive surfaces).
Years ago there was some talk about different dyes (or lack thereof) causing some colors of towel to be softer than others. I never experienced that and I don't hear that piece of trivia any more, so either no one cared, it isn't true anymore (due to mfg. technology changes) , or it was never true.