(1) It looks like can has got some impurity in the water (although there shouldn't be any impurity in the water, if it's really distilled water) or in the container. I agree with Kerik that as long as the solution itself is still bright yellow-orange, the filtered solution should be fine. (BTW, I've never seen anything like this in all the years I've been gum printing).
(2) Light doesn't have any lasting effect on dichromate by itself; there must be some other material to participate in the reaction. Without a donor material to participate in the reduction of the chromium the reaction doesn't occur; that's the role gum arabic plays in gum printing, is serve as a donor to facilitate the reduction of chromium. The crosslinking of the gum, which is the foundational principle of gum printing, is a collateral effect.
(3) As to the green filaments in can's dichromate being a precious pigment... well, I'm somewhat skeptical of that assertion, but would be glad to be enlightened, if it can be shown that this is the case. But since we don't know what the impurity is or how/whether it's reacting with the dichromate, it seems rather unlikely that we could say anything definitive about the product.
Katharine