650nm is approximately red. It depends what other light the sample absorbs, but if it only absorbs light at and around 650nm, it\'s pretty much going to be greeny-blue (because the red is absorbed, the green and blue are reflected back or transmitted through. Solution 650nm is approximately red. It depends what other light the sample absorbs, but if it only absorbs light at and around 650nm, it\'s pretty much going to be greeny-blue (because the red is absorbed, the green and blue are reflected back or transmitted through..