If you notice, the design is still the same but the color is different.
One of my clams is half gold half light green.
It's because half of it's body was being covered from the lighting so it caused the pigments in the mantle to change in color.
If you notice, the lighter portion is the side that is usually blocked, while the left side is the natural coloration on the clam.
I've noticed this on 2 of my clams, but once you leave them back on direct lighting for a few days to a month the color comes back, but it's still noticebly in a bi-color.
You too can make your bi-color clams.
Try it out!
I wouldn't recommend it, haha it was just a freak accident.