Getting Solid thin Walls without innefficient fill

I created a simple box, with walls of 1.05mm thickness - trying to match to my nozzle size of 0.35mm.
My hope was that by using a Shell Thickness in CURA of 1.05, I would get 3 straight-line runs on each wall to get the (3 X 0.35) thickness of 1.05mm.
Instead, it looks like CURA will always leave a gap between the outer and inner walls, and then - if i want to solidify the walls and use FILL of 100%, the pattern it uses to fill is the very innefficient back-n-forth filling, rather than using straight lines as it would with the shell.
The screen shot shows what I mean…
Any guidance on how to force CURA to give me straight-line runs on the walls of a thin-walled box?
BTW - What’s the difference between the green coloring on the layer view in CURA versus the yellow?

I discovered that by using a thikness of 1.04 (one hundreth less than the wall thickness of the model) it seems to at least show solid walls in CURA (haven’t tried printing that yet… but that only worked on the simple box (left side of screen shot) not the complex multi-compartment box (right side of screenshot).

I discovered something CRAZY… and improved my print speed by 62% on this model in the process…
wrote about after doing more experimentation here: