What Do You Mean by Blue?

I have from time to time had to deal with the epistemological issue of; what do you mean by blue? It seems that in the small but combative world of daylily fans there is the debate as to whether or not one can grow a blue daylily.

Now it eventually begs the question of: what do you mean by blue? I have written on this issue but alas the doubters remain. I have just read a brilliant paper on the Costa Rican river called the Sky Blue River, and it is a brilliant paper. It seems that there are two rivers in the country that when they meet the pH changes just enough and the molecular content of each river changes by the same so that the result is a brilliant blue river.

The paper by Castellon et al is superbly well done and complete. Simply the molecules from one river combine with those of a second and form an almost uniform molecular size molecule at about 566 nm and thus reflect the light back at a very narrow wavelength, the brilliant blue color.

For any of you who are interested in a wonderful explanation of a natural phenomenon this paper should become a classic!

Castellon, E., et al, Scattering of Light by Colloidal Aluminosilicate Particles Produces the Unusual Sky Blue Color of Rio Celeste, PLOS, September 2013, V 8, N 9.