A number of factors help determine when you should paint your home’s exterior. These include your local climate and weather conditions, the age of your home, and the type of siding used. A high-quality finish in ideal conditions could last 10 years. But if your home takes a beating from the elements, you may need to repaint as often as every three years. Most homes can be on a 5-8 year interval. If you’re not sure if your house is due for a refresher, watch out for signs of deteriorating paint, such as fading and chipping.
I agree with JHs. If there is no new color on it at all, just talk to the painter about it, if it was an honest mistake (which can happen very easily while painting) your painter should have no problem fixing it. However, in my years of experience, it is not unusual for 2 coats of door paint (good quality) not to cover very well at all. I once painted a red door 7 times, plus a tinted prime coat before I found the door to be a solid color.