Most would realise a black car feels a lot hotter to touch on a sunny day than a white car. The same happens to your front door when you choose a dark colour.
The effect this has on your front door: A black front door in the hot sun can get up to around 70-80 degrees. If the inside of your house is around 20 degrees, this is up to a 60 degree difference between the inside and the outside. The next thing to consider is the thermal expansion of different materials. Aluminium has a linear temperature expansion coefficient of 21-24. Using a calculation, we work out 2.4m length of aluminium with a 60 degree increase in temperature, will grow around 3.3mm!! And when the inside stays around the same in temperature, you can imagine the force the outside face has, trying to bow the door. As soon as the aluminium cools it will quickly shrink back and thus the door goes straight again. The other thing to remember is the bigger your door is, the greater the thermal expansion and thus the more the door will want to bow.
Now if you look at some other materials: Wood has a linear temperature expansion coefficient of around 5, one fifth of aluminium which means timber will not have the same force trying to bow your door. Steel is around 12, glass 6 – 9, Fibreglass depends on the chemistry and glass fibres. Parkwood Duramax doors are around the same as aluminium.
The hinges on a door will keep this side of the door straight but on the lock side when the outside wants to bow, will leave a gap top and bottom when it pulls away from the jamb seals. For an opening out door this wont be a problem as the door will want to get tighter against the jamb seal but may mean the door is hard to shut. As most homes have opening in doors, I would recommend using a 4 point lock which has shoot bolts top and bottom which will help hold the door straight and thus keep a good seal against the jamb.
If you live in a warm climate, get a lot of hot sun on your front door, I would suggest either, a non-thermal door (it wont bow as the inside temperature of the door will be similar to the outside), paint your door a light colour, or use a 4 point lock. In a colder environment I suggest either door with some thermal performance but a light colour if it gets sun on it. Click here to learn more on thermal expansion.