Thank you all for your help! The same day I asked this question I researched a bunch of titles and finally, actually found some comparables. I learned a good bit about the language of WWII-novel covers in the process. Government or otherwise pillared building in the picture = spy novel.. Black-and-white with a few pastels = women's fiction with a contemporary woman finding out family history or something. Black-and-white with splashes of strong color = suspense/drama on a smaller scale. That would be mine.

Anyway, thanks a ton!