You can unlock a bunch of different coloured Yoshis. On the file select screen hold up on the d pad and hit start. That gets you to the scanning screen. You can google the QR codes. I think IGN has a page with all of them
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Sorry pal, but this is the moment I've been waiting for. I have to do this or the anger inside, will not go away.
There's blue, red, yellow, light blue, pink, black, and white Yoshis, plus a Yoshi costume for your Mii. The North American White Yoshi code hasn't been released yet I don't think, but all the rest are out.
-- SuperNiceDog didn't have to reconcile his name... But Dauntless Hunter is now MrGreenonion