Do you say colorful or colored shirts?

Answer 1

It depends on what you mean.

Were the shirts filled with lots of colors and maybe interesting designs (like Hawaiian flowers or something)? Then use colorful.

Were the shirts dyed so that they were not black or white? Then use colored.

Answer 2

Colored shirts

http://www.google.com/search?q=colored+shirts&hl=en&prmd=ivns&tbm=isch&tbo=u&source=univ&sa=X&ei=BOjcTe3_A8rr0QGVw6DCDw&ved=0CGAQsAQ&biw=1024&bih=413

Answer 3

Colorful shirts

http://www.tiedyes.com/tiedyedteesrf.html

http://www.ed-hardy-best.org/images/ed-hardy-mens-shirts/ed-hardy-colorful-shirts-online-sale.jpg