I reall like the current colors and your red roof. I think you can change the house colors and not change the fence color. Here is one example that is in a tan family: With a white trim and dark brown shutters, I think it would work. Here is another example of a tan shade: I also like this light grey with white trim: Would you consider a green base: Then chose either a brown or red for the shutter.

As the appearance of the garden has a modernist style with the straight lines and concrete furniture how about a Mondrian influence and add a bold strip of blue? It is a pond and with the right shade it could look really relaxed and contemporary. My daughter's suggestion is a chalky lilac!

I once saw a gorgeous grey house with a chartreuse door and lots of purple plants in the front of the house. Wouldn't work my (horrible) salmon pink house (one day it will be painted) but since you have the grey might be worth considering?

Something like this would be great!