Crystal, I love the painted rocks the most but the wiffle ball is a wonderful idea! Fun ideas!!
As for your brown house, you are right, it needs to stay brown. I love the cabin feel to it.
Your car color is a great direction to go! Blue! I know you did not mean that but I love blue with green plantings.
I would not think of your house as a color but as a neutral backdrop like dirt. Adding green plantings (earth), blue (sky and water) and yellow (sun) would be lovely. You could also someday stain the house a darker richer brown if you have nothing else to do.
