The red light would be the pressure switch, the yellow would be the level sensor. Make sure the shop put the right part in. The switch is on the back of the oil filter housing, and the level sensor is in the bottom of the oil pan.
If the light only comes on at idle, or low rpm, then I'd believe that the pressure is a bit low at idle (due to the oil pump turning slower), so I'd make sure the oil filter isn't plugged up with sludge. An oil change may be all it needs.