The kinematics of the GPM stars with known B-V colors was studied with the Ogorodnikov—Milne model of a three-dimensional differential velocity field. The technique based on the representation of proper motions by means of orthogonal functions was used to derive the parameters of the model It was found that two samples of stars with B-V < 0.55^m and B-V > 0.55^m have different values of the Oort constants. In addition, a differential deformation of -0.0030±0.0005 arcsec per year parallel to the galactic plane was detected for the first star sample.