This may be hard I’m not sure, afaik Odin simply uses Unity built-in styles to retain a ‘native’ Unity look. However, I think something should be done regardless, the current contrast of UI elements in light theme is really bad and hard to read visually.
I made a very quick and dirty mockup to illustrate how it could be better:
I also know that Unity 2019.2 or 2019.3 is bringing some refreshed editor theming, although I have no clue if it will address some of this. Me I’m just logging this issue so it’s not forgotten about, so I’ll leave you guys call the shots. Just know that this has been very aggravating for a while now, and I remember some other members of the Discord community complaining about this as well. I wouldn’t mind the forced Unity light theme so much if it didn’t make information that much harder to parse. Considering that Odin Inspector is essentially hijacking the entire rendering of the inspector, I think Odin should also take on the responsibility of maximizing the readability of the presentation.