Change selection background color
The default yellow shade is two bright which make the text unreadable after selection. I'm currently using #5E5B3C which gives a better contrast.

This is same on both MacOS and Windows
Thanks for reporting @gayanper .
This is related to https://github.com/AObuchow/Eclipse-Spectrum-Theme/issues/116. Spectrum Theme's text selection on mac is objectively unusable, and I find your suggested color much more appropriate for Mac OS until the underlying upstream bug is resolved.
From a subjective standpoint, I like the current look on Linux/Windows, with a yellow background and black foreground:

This is same on both MacOS and Windows
However you said you find this issue also occurs on Windows, so we might differ in opinions on the yellow/black color choice, but that's ok :)
At the very least, I could add custom CSS for Mac's only to change the selection color to #5E5B3C as you suggested, What are your thoughts on doing that?
Hmm may be if this was decided intentionally may be i can change it and let oomph to sync over my workspaces. if you think the same let close this issue.