Colour coding the books in your shelf is not something to be afraid of. And don't you dare think it's silly! Putting books in order of colour seems completely irrational, especially if you know the Dewey System. But I'm a very visual person, and tend to remember the picture on the cover of the book or the typography on the spine before the author or title jumps to mind. But maybe that's just me.
Plus, it looks great! Especially if your bookshelf is in the lounge or family room of your home, where you see it all the time, you need to spend a little extra time in 'dressing' your bookshelf. Now not everyone has the skill, insight, patience or time to place memorabilia, books, flowers or trinkets in clever configurations to make the bookshelf look good. But as long as you are not colour blind, this is a neat trick that will make your shelves look instantly 'arty'.
I've done it a couple of times, and love it. You won't be disappointed!