First, you want to hang a gourd to ward off evil spirits. Second, you want to give the gourd as a gift to your friend, and wish your friend good luck. Third, you think different colors of gourds have different functions.
But, I tell you:
First, from ancient times to the present, gourd, as an instrument for regulating geomantic omen, generally uses copper gourd, and it is self-evident what color copper is. As a musical instrument, copper gourd's role lies in the shape of copper and gourd, not color. Therefore, the color of hanging gourds is not particular.
Secondly, as a geomantic tool, the gourd is mainly used to curb, drain and collect the big evil spirits and wind evil spirits in Huang Wu. If you don't know what evil is to ward off evil spirits, hanging a gourd may not be effective, because everything has its vanquisher, not a gourd can take away all evil spirits.
Third, the color of gourd has no substantial effect on exorcism. Besides copper, gourd as a gift is also a psychological suggestion. Crystal is a blunt thing, and it is made into a gourd to ward off evil spirits. So, should it be the throttle or the brake?