Most currently used models of filters like Bayer filter (Fig. 1.) has a number of green pixels equal to the sum of other two components (red and blue). The main goal of such a solution is to approximate the sensivity of the sensor to the sensivity of the human eye, which is the most sensitive to green component of visible light.
Fig. 1. Bayer arrangement of color filters (R, G, B)
Photosensitive elements from CMOS array are coated with RGB color filters according to the Bayer pattern (Fig. 2.). Each element of the matrix passing only one of the three components of visible light (Red, Green or Blue). The values for the other two components of a given pixel are calculated based on the values of neighboring pixels in the process of interpolation.
Fig. 2. Picture from the C3088 camera (RAW)