Convert_to_webp_lossless results in strange colors

[vladimirhacker]

Converting jpegs to webp changes its color to different. Example here: https://hdrmaps.com/nettle-weed-atlas-1/
As this is a live site I have chanegd background to one matching new image #1f1f1f.
Converted image should have background color: #202020, but it has #1f1f1f
When I turn it off it's ok. I have noticed it on all images.

[Lofesa]

What do you mean with background color? css?
I can´t see any diff between pagespeed enabled/disabled