Header color overlays header image (renders invisible)

I have uploaded my own header image to a WordPress blog — it is the same size as the default template’s header, and it uploads fine. However, I can find no way to disable the color overlay that the default template also uses. I can go into Editor mode and try to edit “style.css” — removing the header color, replacing the color with “none” or anything else I can think of . . . but nothing changes. (Why, BTW, are there two different sets of code for the header, footer, page, . . . one under “Typography & Colors” and the other under “Structure”? Does one have to edit the header in both?) When I select Header Image and Color mode, it shows the same colors as before. I can change the header color in this mode, but I can’t find a way to have no color. As long as any color is there, it obliterates the header image I uploaded. This seems as if it should be a very simple thing to do — but nothing seems to work. I would greatly appreciate any help you can give!