Can you please bisect this? Screenshots alone don't really give us anything to work with and "closed beta" sounds like there's no way for us to actually test this oursevles.
Would it be helpful to get you a steam key? If so, how many would you need?
I'm not familiar with bisecting those issues yet, so I'd either need help with that or time to dig into it.
Looks like this got fixed with one of the recent updates. Proton 5.13-4 has good performance with Everspace 2 on the DX12 renderer and the colors are correct.
proton 5.13-4x1 2020-12proton 5.13x1 2020-11proton 5.13-1x1 2020-11proton 5.13-2x1 2020-11
With Proton 5.13-2 RC and now the released version of Proton 5.13 the colors on the DX12 renderpath in Everspace 2 (currently closed beta) have changed. Before (e.g. Proton 5.13-1, 5.0-10) the colors where correct, just the performance was subpar. Now with 5.13-2 the performance improved a lot, but the colors have changed.
It now looks like this with DX12:
https://steamuserimages-a.akamaihd.net/ugc/1680367456958732460/673443D970F0823865DE47CFBFD7D77D6256E6C0/
It should look the same as with DX11 (launch parameter -dx11):
https://steamuserimages-a.akamaihd.net/ugc/1680367456958733458/9F37F7D3729858844A785362262F56370A8369A1/
My specs: Ubuntu 18.04.5 LTS, nVidia driver 455.38.