Scrolling this subreddit makes me realize I have a lot of STRONG opinions about people's bookshelves and maybe that's not a bad thing?? A shelf full of tchotchkes in front of your book spines (i.e. blocking access to easy retrieval) is deeply unserious stuff if you ask me.
I have always hated shelving books by color. Instant ick from me. If it's not aiding in retrieval, I'm assuming you are more into books for the aesthetics than for actual functional information.