I had not noticed this either, as my default colour is gray 
Sorry folks - however, the only change that should have happened is to the default “unset” colour as it picks grey in that case. On the road at the moment, but I have a bigger fix prepped which switches from passing colours internally to passing styles (thereby allowing optional foreground colours) - this requires a bunch more changes to existing code, so I would suggest a lighter patch in the meantime, I will try and PR asap.
The rest of the colours were copied verbatim from the original code, so if you are seeing other changes to the default theme, then either there is a separate issue (either due to standardizing on the crossterm Color or a copy/paste error by me) - please shout out!