I'm in the middle of working on a project that is similar to the image I have attached. I'm trying to make a background like what they use on it. I have already made my lines and spaced them out evenly. I have also already have my color swatches made up. I just cannot for the life of me figure out how to fill those spaces. I try to connect the curvy lines with the bezier tool and fill in that area but it just fills in a box and ignores the curve lines that I am using. Any advice?

I would probably do it like this

Hopefully the graphic is clear enough