VGFacts

Xiaomu references Mario Kart's Rainbow Road near the end of the Maidens of the Battlefield chapter when the characters are talking about a rainbow you can walk on.

Timestamped for your convenience: http://www.youtube.com/watch?v=-SRrnj7WB0M#t=01h23m40s

Rainbow Road on Mario Wiki, if you don't know what that's about: http://www.mariowiki.com/Rainbow_Road

I don't see how this is a reference to Rainbow Road?

I dunno, it seems like a reference to me, when Xiaomu mentions you could "bust out a go-kart if you wanted". It's an obscure thing to say about a rainbow without it referencing a karting based game.

My mistake, I thought he was talking about text from another character.

I'd rather you link to the exact moment the reference occurs when posting a timestamp. It removes any chance of mix-ups.

Okay I just added an image. It's the same one I provided as an attachment.

The reason I linked straight to the beginning of the discussion is so that the whole deal with the walkable rainbow would be explained.