Rit is a combination of two types of dye and one of them is acidic. It's necessary to use acid dye to color nylon. Salt is added only when dyeing organics such as cotton.
The instructions on Rit dye say to thoroughly rinse when the dyeing is finished, then wash the piece in detergent. This should remove all traces of acid. Thorough drying is important and the process can be greatly sped up by shaking the body of the light hard and often in an up and down arc (imagine cracking a whip). Let it sit vertically for a while and do it again. The next day do it again until all the water appears to be gone. Then let it air dry. For some reason, more water seems to come out of the tail end of the body than from the front.
I've dyed quite a few lights now and done all of the above. I haven't noticed any problems yet but I'll keep an eye peeled.