Red markings - stop do not use or fire live ammunition
Yellow markings - worn, probably not accurate but safe to shoot
Green markings - 2nd or 3rd line weapon (maybe Cadets) in spec & safe to shoot
I've always known those to be Australian standards. India DP markings are typically a wide red band with a white or cream colored stripe in the center. I don't recall seeing those marks on a 2A1 before.