Since you have so many unknowns, it seems to me you will be much better served to find a designer who has a computer program that will show you what changes will look like on your house.

These types of computer programs are available for anyone to buy, but the good ones are expensive---several hundred dollars to start.

They use actual pictures of your house. Then, anything can be changed. Windows, trim, doors, roof line---anything. Colors also, of course. My wife and I bought an inexpensive program($60) that does not do all that, but we could insert a picture of our interior rooms and change colors. Helped a bit.

The garage and it's poorly thought out bump up torpedoed the Colonial Revial facade long before the new windows ever did. No decor changes will fix what feels wrong here. It's an architectural issue, not a decor issue.

You might as well go with the direction that the home currently trends toward, which is modern, especially since you aren't going to change the windows. I think if you redid the roof as a flat roof and concentrated on "color blocks" and other rectangular and linear shapes, you could manage to pull what's there to the modern side.

You could also redo the garage bump up area by making that roofline shorter and smaller and "nest" into the main gable end rather than being on the same plane. Turn the windows into dormers and do the whole addition in a darker color for it to recede from the main box of the house and that would take it back to the more traditional side. You would still need to change the windows to a more traditional muntin look or add muntins to the existing windows.