theory11 — Magic Tricks & the World's Finest Playing Cards

Shirts for DressCode

Honestly i don't believe it matters.. Just use different colors to make it more spectacular, don't change from a black shirt to another one that's also black.. I'd still work but something like black to red would be more wow-ish.
About the length, Calen covers some details on the dvd i'd recommend you re-watch it. :)

-Johnny
 
Like Johnny said, Calen will go over what shirts are good to use. Plus you can experiment and find shirts that work for you. It's a dirty effect, I highly recommend it.