<image>A person has 3 colors of light bulbs (there are enough light bulbs of each color). They need to install a light bulb at each of the 6 points A, B, C, A_{1}, B_{1}, and C_{1} as shown in the figure, with the requirement that the light bulbs at both ends of any line segment must be of different colors. How many different installation methods are there in total? (Answer in numbers). 
