What type of dye should i be using? Rit?

I need to tie dye my light purple shirt with dark dye for my cl shirt, and i've heard about Rit dye but im not sure about it. Is this the best dye. I want this to look really like crazy epic, so does the Rit colors come out well? Also i've never tie dyed anything before so could someone please post a link to some beginner instructions, that would be terrific! thank you