Haha, I totally forgot about the spines thing
The color thing comes from the volume covers and artbooks. The manga wasn't colored by Araki, so for better or worse, the colors are realistic/consistent. (So Morioh has a blue sky in the digitally colored version, despite being yellow in the anime.)
People like the colored versions since, well, Araki goes crazy in Part 5 and 6, and most scans of the b&w version on the internet are not high quality, so it's kind of hard to make out what's going on. And the coloring job for parts 4, 5, and 6 is really good. (It's not as good for 1, 2, 3, 7 and 8, so read those colorless.)