Exercise 2 solution

Add lines to the sources dictionary, for example:
    "Heavy overcast (your source)": <value>,
The script labels anything at or below 3000 K warm-looking, 5000 K or above cool-looking, and the rest in between.
Compare with the article: it calls 2700 to 3000 K warm and over 5000 K cool, so the first two bands agree; the in-between band is my simplification, not the article's.
Always name the source for each kelvin value, as published figures vary (the chapter shows two pages disagreeing on the sunrise figure).