As an experienced dyer I am going to have to respectfully poo-poo the RIT suggestions. Partly because it is an all-purposefully crappy dye and partly because there are better and simpler alternatives out there.
Your best choice would be a fiber reactive dye. Though fiber reactive dyes are made for natural materials, specifically cotton but I use it for my silks too, if you item has a mixed content i.e. cotton/poly, it will dye it too. Just not as vivid. There is no need to boil your project in a pot. Per ounce it is also cheaper than RIT.
You can find it online at http://www.dharmatrading.com/html/en...lnav=dyes.html
. Dharma also has great directions for vat dyeing , which is what you would do to get solid colors. I do my vat dyeing in in those medium sized rubbermaid storage bins. For larger dye projects the washing machine can be used to. Don't worry, it won't ruin to machine.
Here are dharma's directions http://www.dharmatrading.com/html/en...es_tubdye.html
If you don't have time to order online most fine art stores will carry Jacquards fiber reactive dyes. Check Joans too, they may still carry Dylon cold water dyes which are also fiber reactive dyes.
If you have any questions, feel free to convo me.