Color Bleed

Definition: Color bleed occurs in melt and pour soap when the color you've added doesn't stay where it's supposed to - when the color in an embed or section of of the soap "bleeds" or "migrates" into the section or part next to it after it is made - usually after couple of weeks. The blue in the blue layer starts to "leak" into the white layer...or the red in the hearts (pictured) starts to bleed into the clear soap base.
This happens primarily with liquid dye-based colors - but can happen with any colorant that is water soluble. Red is often the most problematic. Non-water-soluble colorants like oxides, pigments and micas will not bleed, but they do not provide bright, vibrant colors, and aren't as transparent. The red of an oxide is more of a brick red; the yellow, a mustard yellow.
Several companies sell what are called "non-bleeding" colors. I have had mixed results with them.
Again, the key factor is whether or not the dye is water soluble. If it is...it will mix in well, be clear, and likely more vibrant. But, it can bleed...
Using a pigment, mica or oxide won't bleed, but the colors won't be as vibrant.
The new "non-bleed" colors are complex combinations of dyes, pigments and polymers. Very interesting things.