Anything is possible, alot depends on the size and color. Remember the lighting could be playing a part in making the clam look different. Also if you look at the clam from the top of the tank down the color will look different then if your looking at it straight on from the front of the tank. You would be really surprise at the different colors you can see from the 2 different views.
Speaking of Clams FishTown has a really nice Tear Drop clam, probably 6"-8" for $79.99. It had a great pattern to it and not really like the normal tear drop pattern. If you have the room differently worth getting as it really different.