A Knightmare is crouching just behind a large tree, keeping within its shadow. It's not invisible, but it is a little harder to see than it probably should have been in this location. The metallic exterior does not seem to reflect the light, and it seems to have a greener hue than it did five minutes ago. Now. Others might speculate: Why does Lelouch not make the entire frame invisible? Answer: Maintaining full spectrum invisibility is an arduous process for an object this large. In comparison this was a mere parlour trick, so he could spare his strength for the battle ahead.

-Lulu's Bizarre Rebellion Chapter 34