I have practically no UI while playing the game, so I’m wondering what all of your opinions are about whether the color scheme of the game background and sprites should be similar or completely separate from the menu UI?
You need to have a “familiar” concept to your UI, compared to the actual game. Make the UI an extension of the game…
We use default UI look 
Not a singel time have anyone told us UI is bad. Example
On the contrary we have gotten positive feedback on the UI
Concentrate on the things that make the UI good, superficial stuff second
Again with the hijack. He did not ask you about your game. But since yer gonna do it…frankly your UI has the same effort the rest of your game does. Beyond the basic info an enterprise programmer may give his insurance client it has about the same presentation pizzazz. It has no notion of warfighing or military ops to it. Standard dark vanilla.
OP. Don’t do standard vanilla out of the box UI look. For most/all games it is the wrong choice. The first thing it indicates is lack of creativity. The second thing it indicates is that the folks put the game together do not have alot of coding chops. Third is that the UI/UX is an afterthought.
Dont have too much UI while in game. This is a classic noob mistake. Having every single edge of the game window occupied with UI info. Its bad design.