@Gargron What you could do fairly efficiently is take the most prominent color:

1) Read bitmap into number array via hex
2) Sort
3) Split into 8 equal array chunks (enough for nearly any album cover)
4) Average each chunk
5) Compare in pairs
6) Discard least-like pairs
7) Choose the first index from the highest number chunk of last pair (they should be side by side)
8) This will be from the middle of the largest color block

You now have a representative color from the cover.