No! I never alter the appearance of any marble in my photos. However, I do use an LED light box to take pictures with, and that sometimes causes the marble to appear brighter in photos than in hand.
If I feel the colours in the photo are way off base from the true colours of the marble, I will either try to adjust the brightness or state this in my description.
The photo grids I use are mainly for convenience, so you can quickly see all sides of the marble in one shot.