You must’ve done something wrong. Anywho, check View>BackgroundNormal/Alternate and adjust the colors in the color file.
Here’s an example of your theme with an orage alternate background:
Ich bin Flame, also werde ich mein Bestes geben. 1) ~/.local/share/color-schemes/theme 2) scrollen nach Ansicht 3) Hintergrund Alternative 4) ändern rgb.