Aiming to increase the data rate in screen camera communications, we intend to define symbols to be used in an M-ary color shift keying modulation scheme. With regard to the R, G, B format of a JPEG image, we generate arrays of colors and acquire their image with the back camera of an smartphone. Then, we select those colors with the minimum error distance and elect the desire set of colors from their constellation space. Given the grouping pattern of the processed data, we believe it is a valid method for defining symbols in CSK modulation, although it needs to be validated for higher order modulation schemes.