Pause
Most slicers let you pause at a layer. Some take a plugin some have it built in.
Slice the object. Pick where you want the pause. It is different for different slicers. Google will probably find it for your slicer. You can have multiple pauses.
After you add the pause, or pauses, yoou generally have to reslice the object.
Now print. The print will stop at the place you put the pause and you can do just about anything you want.
The most common thing is to put lettering of a different color on top of an object. Create an STL that has the lettering sticking up from the object. On the top layer, or layers, the only thing you have is the stuff you want in the other color. When the print pauses, change the filament to the new color. Let the print continue.