In a small bowl or teacup combine the oils and food coloring (don't worry about mixing them together), then mix in a few tablespoons of salt to absorb all the oil and color.
Combine the colored scented salt with the rest of the Epsom salt, stir till the color is uniform, then pour into your container.
If you prefer fizzy salt add up to one cup of effervescent powder (a mix of equal quantities of baking soda and citric acid). You may need to add a few extra drops of color and essential oil, but do not add more jojoba oil or the mix might clump -- in fact, over time, fizzy salt will probably clump anyway, but it will still be perfectly usable.
(See my alka seltzer instructable
for notes on citric acid)