Dark color infill is visible behind lighter colors. Is there a way to prevent certain colors from being used as infill beyond their own colored object?
You can see the dark blue infill behind the Pink areas about halfway up the model. The other infill colors would have worked better. Ideally, I would prefer that the infill match the surface colors to avoid this issue - in this case it added no structural value to the object. In some cases, I can see this being beneficial.
What settings in PrusaSlicer can I leverage to prevent this in future prints?
Some people exploit this phenomenon to get extra shades - look up hueforge for a way to waste loads of filament trying to print pictures a tenth as well as a cheap inkjet...
When designing coloured parts it is common to keep to just one or two layers in order to reduce the number of filament changes but if true-colour is essential design the part with sufficient depth to ensure no shadowing.
Attached is a two-part model to demontrate the technique; unzip, load both .STLs together as parts, allocate a pale filament for the text and a dark one for the body.
Cheerio,