Hmmm...don't think I have ever noticed it myself. Yeesh! I'd assume that it'd be more visible in hatchlings as their skin is so transparent you can see the organs. Definitely something to look out for when I look at them.
As for the black patches, you should snap a pic and post it. Also, you don't have to thank me for the house snake. You're doing me a favour by providing it a good home.