Worms changing color

I have noticed that some of my worms are turning light pink. Anyone know why this might be happening or what it means?
Thanks!

hoggie it happens...my original culture of red wigglers came from a neighbor's leaf compost pile in Kansas. I used and have always used peat moss as my media of choice based on what local worm farms were doing in that area. The worms originally were small (generally under 2-inches) and were a dark red color. It didn't take long before they started growing in size and changing color to that pinkish color you mentioned. I not only use red wigglers to compost kitchen scraps in plastic bins, but I use them to compost horse manure from a nearby neighbor. When the ‘vermicosted’ horse manure was used in holes dug in the garden for tomatoes, peppers, squash, pumpkin and cucumbers, these worms would revert back to their original color and size if they survived the harsh Montana winter, which some actually did. So to answer your question I would say diet and growing media are the primary reasons for color change.