Looking for an easy way to color your bath sea salts? This short video may help. The "Sea Salt Dyes" from GoPlanetEarth.com are exceptional. They are a special blend of glycerine and FDA approved lake colors and come in a concentrated form. A 50/50 ratio of water to salt dye can be added to thin it down.
It's OK to use regular tap water. The water will make the product less intense, and easier to blend into the salts. Because glycerine is a natural preservative, you may dilute the product in advance and keep it on your shelf with no fears of it going bad as long as you dilute the salt dye with no more than half water.