First, the top image is the sun in false color representing, if I remember correctly, seeing it in X-ray radiation. Stars with their blackbody radiation's peak frequency at that of the color green appear white, and completely white. "Why? White is a different color!" you might say, but the thing about that is that that is only the peak frequency the star emits, aka the one it emits the most of, but because of the way the blackbody radiation works, distributing the "frequency curve" over many frequencies that together we call white, so although the sun emits mostly green, we don't see a green star when we look up in the sky, we see a white one. Therefore we don't have green stars in US2 (yet) because it's not exactly realistic (barring having a star with a very strange chemical composition but that wouldn't really make sense until we can add the elements that might make it do that)
Second, they plan to add these things anyway (they even said so in their roadmap) so...why request a feature they've already confirmed to be made happen one day?
Third, most of these things are very present and very fixed in UNiverse Sandbox Legacy. If you refuse to use US2 in its current state because of the bugs not being immediately fixed (which is something that literally cannot happen without the development process taking much too long. Sometimes its best to leave a bug be for a while since it doesn't break anything's functionality and so that you don't have to completely re-debug it whenever you do add features that do break things) then just forget about the higher visual and in some cases physics computation quality in US2 and use US Legacy. Let the devs do their thing, they'll do it better if you do.