In the field of classical Feng Shui, a main door which directly overlooks a flight of descending stairs rates as one of the most inauspicious signs for the occupants of the home.
Not only will money become a serious problem when the owner cannot seem to invest wisely or even accumulate wealth while living there, the longer the staircase, the worst the ill effects. Occupants could even be forced to vacate the property as a result of the accumulated ills they incur whilst there.
In Feng Shui, qi is the life force that permeates and surrounds all matter on the planet. The goal of feng shui is thus to harness the positive qi that is inherent in a certain setting in order to endow occupants of that property with wealth, health and happiness. In any home, the main door serves as a 'mouth of qi' because it acts as the gateway between the external surroundings (yang) and the internal setting (yin) of the home. The aforementioned predicament of a main door facing a descending staircase - known as 'pulling nose' - can be avoided by following some simple but effective rules.
It's important to allocate a spacious area just outside the main door. This bright hall encourages positive qi to gather before it is ushered into the home. When the bright hall is cramped, good qi cannot gather, which directly results in poor Feng Shui for the occupants.
Once you have allocated an area for your bright hall, you must inasmuch as possible ensure that it is on a flat surface. Because qi flows like water, if your main door faces a set of descending stairs or a steep driveway, your good qi will flow away like water from your hands.
Similarly, you must ensure that the area directly after your main door within the home - your internal bright hall, which extends about ten feet from the main door - is also spacious. A wall or pillar immediately after your main door merely serves to obstruct incoming qi.
Finally, stand in your doorway and look out. Are such obstructive features as pylons, lampposts or trees aligned to your door? They are negative features in feng shui because they impede the flow of qi into your property. Do remember however that if they are more than 20 feet away, then they should not be considered a problem.
Once you have made sure that your door is at its most effective in optimising your feng shui, go ahead and paint it any colour and make it any size you wish, as neither colour nor size positively or negatively impact your Feng Shui.