Yes, make sure you use at least a couple of packs.
MUST be boiling water, tip a couple of kettles full into a bucket (e.g. enough to cover both halves of the shell) and then drop your plastics in. Stir them every few minutes so the dye doesn't 'pool' in one area and make it uneven.
After an hour or so, take them out and rinse them - voila!
I did the tray, feedneck and both shell sides. It makes more of a 'tint' than a complete colour change but by increasing the amount of dye you use and the temperature of the water (hotter = darker) you can darken the colour.
Good luck with it...