what's up mate
Right Kashi have a amount of nylon in the seat when made - some seats just have plastic with no nylon in them.
Dylon and rit like to stick to the nylon when dying - the more nylon the better the colour
So a seat with just plastic might dye or not ?- it might just have a dull fade colour and turn the seat colour a "off colour"
If the seat is some thing that is not mint or you don't mind trying - well go for it - black is a good colour to dye, as you can leave it for a long time with out a shade change like a red or blue
worth a try if you don't mind what colour it goes to in the end - but if it's a good seat and you think it might spoil it - sell it to some one or swap it for the right colour one
cheers B