A trivial issue for your information.
My Win7 64 bit installation has been modified to show a light ochre background in text boxes by default. It’s kinder on my poor old eyes!
The text in the tutorial installed with Scrivener has been written (presumably) on different machines - so blocks of the text show normally (black text on transparent background allowing the default background to show through) and some blocks of text show black text on white background.
I can’t call it a bug, but it just looks a bit untidy.