We introduce a new non-linear method for RGB-to-XYZ color calibration based on the technique of thin plate splines. Originally, thin plate splines were designed for deformable matching between 2-dimensional images for object recognition. We use 3-dimensional thin plate splines to map between sets of RGB device coordinates and corresponding sets of CIE XYZ coordinates. Tests calibrating several displays as well as a camera show thin plate spline calibration to be more accurate than existing linear or non-linear calibration methods.