I've been looking for some screenshots with english interface (I got it in spanish so not really helpful) to add another option that might be useful in some scenarios, that would be Replacing Color.
I'm gonna use it to get the stats background in black but It can be applied in any place with anything (you can replace the color in the whole pic, a layer, or a selection).
We start with a piece of the common stat screenshot.
Now we head to the main menu; Image *> *Adjustements > Replace Color (as you can see in the next pic).
This will open the Replace Color configuration window.
Replacing Color (RC).
Just a few things:
Trough the dropper we will select the first (and main) color to replace. The dropper with a plus (plus dropper?) will allow us to add another color, or more.
The Fuzziness would be like the color deviation allowed regarding the color/s selected, so take care selecting many colors or setting high fuzziness values, you know, a given color is 'a balance' of basic colors.
Ok, going back to our pic we can see that it has two colors in strips. For this example I advise a Fuzziness value of 25.
Select one of them (through the dropper and clicking on your main pic). Then the little pic on the RC window will change showing in white the area affected.
The best way to see how wide is the area affected (in your main pic) would be setting the Lightness to -100.
Let's go for the other color. We are going to add another color but first, click on the 'plus dropper' icon, and click on the other strip in the main pic.
Once again the little pic on the RC window will change in a whiter version,
but we can see that there still are some black areas in the left border.
Now we can choose one of two ways, clicking again with the 'plus dropper' in a black area (on the main pic) or set a higher Fuzziness value (like 75).
Sometimes one way is better than other, so try it.
Looks ok, click OK and we are done.