Thanks for the note and picture! First of all, I really must compliment the lovely plantings around your front entry way. Really well done!
I hope you had a chance to see the other piece about front door colours and have had a chance to think a little about your choices.
Now to your questions…first we will address the garage door. I AM a big fan of painting garage doors. They are very often JUST what you described…a BIG expanse of white! I think it is a great idea to paint out the doors in a colour close to the house colour, and have it blend in. My husband would say “Why would you paint a beautiful white door like that?” “It is just too much!” is my usual reply…to many of his comments, actually. If you don’t want it to blend in completely, try a colour just a shade darker than your house colour. I do not endorse painting the garage door the same colour as the front door. I know people do it, but that doesn’t make it right.
As to your front door colour, I think that depends on your own taste. Your home is neutral colours now, so technically almost any colour could be applied. A deep red would be the classic choice for a gray house with dark shutters. Orange is my favourite colour, and I might choose to put a deep burnt orange with this gray. I suspect the beautiful fall colours in your photo have influenced that choice! Think about the colours that you love. Then choose a shade of that colour that is deep enough to complement the gray, but also warm up your entrance.