what is the garage door made of?? is it steel or wood?
either type door usually comes already primered. if the door has been previously painted,just wash it and paint right over the old paint,unless there is peeling,then scrape off loose paint,prime and paint.
its pretty hard so goof up a paint job on a garage door,i believe.
unless it needs some special kind of paint for it to stick,which i highly doubt.
as far as the can of primer goes,take it down to your local hardware/paint store(menards/home depot) and have em shake it up for you. then you should be able to use it again. unless the can of primer got frozen,but,by your location,i seroiusly doubt that
as far as choosing colors goes,me and wifey just take a cruise and look at houses for color schemes. or google for house paint sites.(sherman and williams,dupont,etc). they usually have some sort of software prog you can use to look at color schemes.
our house has vinyl siding (cream) with chocolate window trim.(trim is metal) so we are stuck with it. i would like to change the color,but cannot.
make sure to take a hard look at the color of your roof. its the only color that you cannot(cost effectivly) change.
and good luck-keep us posted
brad/draboo