During the light cycle battle, when Sam is on the second level down and looking up, one of the enemy cycles on the first level swings into position to wipe out a friendly. When he does so, his light wall, as he crosses over the blue lines on the grid, is seen as green through the grid lines, a combo of the two colors. I think it was CLU, so his cycle's wall was yellow, so when he passed over the blue grid line,........yeah those colors would combine into green.

These guys thought of everything! Well, I wouldnt've thought of it anyway.