I would not paint a light bulb. That could be dangerous.
I put a 250W red bulb in a heat lamp in my coop each winter. If you want to set the water on the ground under the bulb, that sounds like a good idea. Just make sure the heat lamp is up high and secured in two ways so that it cannot fall and break. For example, you can clip it to the rafters and you can also TIE it to the rafter. Make sure it is not in a place that the chickens can jump up on it. Make sure the cord is not hanging because I have had hens jump up on the cord and perch.
I know there is a ceramic wall heater that is safer and there is a water dish that you can plug in and it keeps the water from freezing. But I put a heatlamp with red bulb above the perch and my hens seem to really like it!