From personal experience, I can tell you that I knew I'd broken the "piggy toe" on my foot after I stubbed it in the middle of the night, then woke up in the morning to discover that while I'd slept the toe had turned bright purple, like the color of grape Kool-Aid. That was kind of freaky. I didn't think that color actually occurred in nature.
Though it did make for a funny scene when I went to the emergency room to get it checked out (just to be sure). When I was wheeled into the x-ray room and put my injured foot on the machine, the tech asked me "So which toe is it?" ... and I replied, "The PURPLE one." Haha