The chapter number is black, but it should be light gray. I have not modified anything in the layout files and have downloaded fresh one. Has anyone got a clue where I can change to adjust the color back to light gray?
This is the code that
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You could add the following to your preamble, which would "reset" the original code at the beginning of the document. So if you (or one of your packages) are responsible for the black colour, this should reset the changes.
Note that this is not a fix. A fix would be to construct an MWE in order to find out how the error occured in the first place.