It's easy-peasy, as Jamie Oliver the cutie-boy says, so go for it:
First mix up your salts. The kind you use really depends on what texture you are going for. I usually use about 1/2 espsom salts, 1/2 sea salt, and a good amount of baking soda. Mix all that together. Add a bit of vegetable glycerin (about a teaspoon for every two cups of salt, I think). You get get vegetable glycerin at a health food store, generally. Then add essential oils and colors of your choice. The color is the hardest part, because liquid color (I use food coloring, because I'm cheap, but you can get special soap colorant at a craft store) doesn't adhere very evenly to salt. The best thing to do, I think, is to mix and mix and mix and mix with your hands to get the color as evenly distributed as possible, and even then larger grains of salt are going to hold more color than smaller ones, so don't be too much of a perfectionist. Scent is really to your liking--I use a little 1/6 dram sample vial of a scent for about 4-6 cups of salts, but it depends on the flavor. You want the smell to be fairly strong when you are mixing it up, because otherwise you have to use too many salts at a time, and the smell seems to fade over time.
For containers, you can use whatever, but my current favorite are old glass containers from the Goodwill, particularly the heavy glass type with latching lids like folks keep coffee and stuff in.
I think I'm going to try sugar body scrub next, so I'll let you know how that goes.