Upload & Sell: Off
I have a set of the filters Vivitar sold for the 285HV somewhere which slip into the slot on the front rim but I never used them much because they were a very limited range of colors. B&H might still sell them.
What I did is bought several Rosco sampler swatch books.
B&H formerly only charged a penny for them but due to demand they were never in stock. They now cost $2 (last time I checked). They are about the same size as a speedlight head and one one swatch book has everything Rosco sells — colors, ND, diffusion materials (what is hanging out in the photo). As you can see even if you don't use the swatches on the flash its a handy reference for selecting them because the slip sheets between gels have the specs on color K° shift and exposure difference.
B&H also sells a larger size sampler for about $20, but for the smaller ones if they don't fit you can just extend them with some black electrical or masking tape to prevent spill.