Green is the color that our eyes see the best. It should still show up reasonably on a brown house. It will not be the same as on a lighter colored surface, but it should still work as long as there is not too much from the projector christmas light or other sources such as a street light. The red however will probably wash out and not be very visible as the two colors are too close in tint.
Just like how a flashlight will reflect less on a dark color versus a light color.