I think it's a bit harsh to categorise the former as incorrect. At first glance I couldn't see any reason.
The only possible reason I can think of is that you're being asked to choose from a variety. Then the example specifically mentions just three colours thereby somewhat nullifying the idea of there being a variety.
The second example gets round this limitation by saying that the three colours mentioned are available (for choice) and by implication the rest of the variety of colours are not available.
As I say it's somewhat technical and opaque but that's the only thing I can come up with.
Student or Learner