I've did 2 dan good results especially dyeing green to black,i had the rails taped up but the heat of the water made the tape come of,after i dried it all off sprayed with wd40...rit dye is the best that i used forget dylon and remember to add salt 
Salt is only used when dying cotton, useless for dying nylon, I contacted Rit, they said for best results add 1 heaped table spoon of non bio washing powder, Rit is only designed to dye within 40 mins, so if it doesn't work after that it will never dye
(all depends on the grade/quality of nylon)
boiling water and salt will only damage metal items including the pot, I know , I've done it.
Don't leave a seat in longer than the 40 mins or the seat rails end up a baggy fit in the seat
