Yes, that lighting should be able to support a clam. As for color Maxima clams are usually blue, Crocea clams are usually a greenish color, and Derasa/Squamosa/Gigas clams range are usually found in green and brown. And if you can find a Hippopus clam you should pick it up because it has such a wierd name and also fun to say
As for size that wont be an issue clams are incredibly slow growing, and it will take several years for it to even begin to outgrow your tank. Maxima or Crocea will be your best bets as they are the most commonly found and tend to do well.