But at this point in time, it isn't just readability, it's because it has been that way and obviously to us, having such a strong reaction, changing the arms to blue is anti-appeal. Plus there's another reason that pink arms could have been selected initially: a rare concession to what hedgehogs actually look like:Silv, obviously there are always times to make exceptions, for stylistic reasons or fashion or function whatever else. I do it all the time in my own work. But that just isn't the case with Sonic. He had pink arms for one reason only, and that was readability, not appeal. Same-coloured arms make more sense from a design and appeal perspective, which is why every single other character in the franchise has them, as does every other classic "rubber hose" character than served as inspiration for him. The blue arms only bother us -- and I am including myself in this group too, they drive me mental -- because we're so used to the pink ones, and because the blue ones were such a common colouring error.
Now consider a design where his hind legs are also pink! Hideous!
And of course, Amy remains the other exception, whose "pink" (not bright pink like her body) arms were not initially needed for readability because 1. She wasn't a playable character and 2. She wore clothes (and still does). Maybe Sonic Team didn't want to change her design, but she (and Sonic) kept their arm color while Shadow and Silver, both "hedgehogs," didn't play by those rules. Maybe Sonic's arms were pink for readability, but besides the perks that Smile mentioned, playing off their own established designs can create interesting results: Both Silver and Shadow are kind of mysterious characters, and by changing their arm color (also un-naked bellies) they emphasize their foreign quality against Sonic's (and Amy's) familiarity.
I am less bothered by the blue arms than I am the idea that they are blue now because that's what they "should have been" from the beginning, because that's "the rules." That's stupid. (Not as stupid as thinking that "Pants Sonic" is a really good idea, but..) Anyway the point of this is that there are reasons to keep the pink arms besides readability and "design rules" and also I am an adult making a passionate argument about the color of a cartoon character's arms so maybe I should have just typed the whole thing in caps and complete the god damn transformation already.