A frequency uniquely defines both wavelength and energy via E=hf and lambda = c/f. So nothing sloppy there.
Although, wavelength changes in a medium (changing c to v). Frequency stays the same, and that's what your eye sees as a color. I assume. If your eye were filled with glass, would it see different colors? I don't think so. So even though colors are usually defined by wavelength, I think it's frequency that is more appropriate.
true that most blues are a range of frequencies. However, a single frequency is also blue. Our eyes aren't very good spectrometers. As such, a wide range of blues can produce precisely the same visual stimulation as a single frequency, so it is at least possible to use a single frequency to describe what we see even if we are seeing a range.
In this case, Danny is using a spectrometer, so he would see the individual frequencies and/or ranges. I had actually assumed that he would see lines because labs tend to have fluorescent lights. He might then have just picked out the strongest line, read it off, and declared the object to be blue. However, it turns out that the "lines" of fluorescent lights aren't as narrow as I thought. So you got me there.
Still, it's reasonable to assume he could have read off an average frequency or centroid value of a range significantly narrowed by the lighting source.
In that case, so many significant digits would then, of course, be both unnecessary and misleading, but that is