They show colour depending on light. They are solidly grey and black. Hit them with a good camera flash from above, and voila, they're blue.
If sunlight hits them, or a space between the plants, they'll fool your eyes, or a camera.
What they lack in colour you'll soon find they make up for in character. They really are cool fish to keep. From what I can see in the photos, they are very young and have a long way to go.