What do I tell the paint store to mix in order to get a color that best matches a wavelength (5040 Angstroms)?
You really can’t make paint that is a perfect match to light of a single wavelength. In this case, the wavelength you selected (5040 Angstroms or 504 nm) would appear cyan, or bluish-green, if viewed in isolation. Since paint doesn’t reflect just a single wavelength, you can’t reproduce this physical stimulus with paint. Even if you could, it would be very dark since it would be absorbing most of the visible spectrum. The best you can do is make a visual approximation. For this wavelength, you could go to the paint store and select the paint sample that is bluish-green (about half way between an ideal green and ideal blue) and as bright and chromatic (saturated) as possible.
