As far as a special app, if it’s just one bulb and the notifications are simple, you can probably just use the official smart lighting feature.
If you want more complex logic like a different color notification depending on who is home, or an escalating notification where the color changes depending on how long the door has been open, stuff like that then your best bet is probably just to use core.
There are a number of individual lighting smart apps if you want to take a look at those. Core do pretty much everything, but sometimes you might want something simpler…
