This does not happen with pure colors. However, most fiber reactive dyes you buy with neat names will be a composite of colors. When these dyes are mixed with water like in immersion dyeing, all of those dye color particles combine and make the solid color. When they are sprinkled on snow or ice, they magically separate out which result in these surprises.
Here are a couple other examples: This piece is dyed with Dharma Forest Green #31A.