What a cute cottage! While you're right that a darker color will make your home look smaller, my concern about gray for the siding is that the shingles are gray and which is what's making everything blend right now.

If you want black shutters, paint the railing, chimney, fascia, eaves, gutters, and downspouts black also. Keep the foundation rock and porch ceiling as is, and paint the body a creamy white like 7042 Shoji White. Then add something fun to the front door that will bring out the rhoddendrons and other plants in your yard. Look at 6312 Redbud, 6875 Gladiola, or 6402 Antiquity.

If you don't mind your home looking smaller, go with a deep gray that's darker then your roof, like 7067 Cityscape or 7074 Software. For all of the details I suggested be black- make those white. Pain the shutters black consider the same front door colors as above.

Don't be afraid to have a little fun with such a charming storybook house. Enjoy!