I was thinking something like the attached mock-up pictures.
"pushbutton_off.png" as the default (Off) state
"pushbutton_activated.png" as the On or Active state, the active image will only show for a second or so before returning to the default (Off) color scheme.
The push button should have a configurable "On state" time. For instance a garage door may only need 0.5 seconds in the On state, for something else you may want to configure it to 20 seconds.