More colour filter experiments

 

After considering the stained glass, I was back with the classic colour filter experiment. As shown above, only blue will get through a blue filter. The other colours are absorbed. This suggests that the scattered light from the clouds contains blue but the tree is not reflecting any blue in my direction.

                                     

Same with the red filter.

And when you put the two together, one absorbs all colours but red and the other absorbs all colours but blue so so see black.

When I've done it in class, they have always pointed out that they can see violet lights. I've never been able to explain that. How can violet light avoid BOTH filters? Is it to do with the intensity of the beam? It can't be ultraviolet because I can't see ultraviolet. I can't find an explanation.