fabric dyes

[amyakieran.livejournal.com]

I was unable to find this information in the memories. As I understand it, RIT dye is a less than ideal fabric dye. My boyfriend is interested in dyeing a fleece lined baby blue flannel shirt brown or blue. I don't have any experience with dying and wish this project be as cheap and successful as possible for him. Is it true that if a fabric is already dyed, as is the case of a flannel shirt, the dye will not absorb as much?

Anyway, any tips for dying a fleece lined flannel shirt would be amazing. Possible dyes to buy?

EDIT: The flannel is 100% cotton, and that's what he wants to dye.