It depends on the panels and the type of switch.
Toggles switch holes are painted.
Rotaries, potentiometer or encoders
The hole is painted but the area around the hole may
be a complete circle or just a portion.
The area may all so be clear or white.
The Intercoms panel with its push pull potentiometer
would be the only panel I know of that the hole is
the light source for the specific switch knob.