[Hammers Nail]

This is what Adobe Media Encoder does when you drag-n-drop a composition to AME’s render queue – saves a version .aep in a temp sub-folder next to the current/last opened .aep version.

Or would be better to write a script that will create a temp folder, and save the project with increment and after done with all, delete them?

[Hammers Nail]

Not sure if I understood what you wanted to achieve, but let’s say try to put this line in the Fill’s Color attribute

UC = thisComp.layer("Ctrl").effect("Up Color")("Color");
DC = thisComp.layer("Ctrl").effect("Down Color")("Color");
S = thisComp.layer("Ctrl").effect("Slider Control")("Slider"); //determines how many times per-second the color will change
if (1-Math.round(time*S)%2) UC else DC;