If you have never visited Crater Lake on a clear, sunny day, then you have no concept of the true definition of blue. Photographs don't do it justice, though images like this one clome close. People will ask what filter you used, what trick of photoshop, but really, it comes down to physics. When the full spectrum of light passes through pure water, it absorbs all the colors of the rainbow, one by one, except for blue (and a few wavelengths of ultraviolet). Blue, rather than being absorbed, resonates with the particular structure of a water molecule, and like the vibration of a damp finger on the edge of a crystal wine glass, the molecule produces in response a clear, pure note of retransmitted blue light. And thus Crater Lake is not just blue in the normal sense, but radiates its own internal light, a luminescence impossible to capture on film. You have to see it to believe it.