Abstract: Methods and apparatus, including computer program apparatus, for calibrating a printer. A color reference is printed for a reference tint. The color reference is a coarse halftone screen printed using a single colorant. A sample for each of multiple tints of the colorant are printed using a normal printing mode of the printer. A user views the printed substrate and provides a calibration input based on the user's comparison of the printed samples to the printed color reference. The transfer curve of the printer is modified according to the calibration input. A color sample and a color reference both based on one colorant are printed for human visual comparison by printing the sample and the reference simultaneously on a substrate, the sample surrounded by the reference, the reference being printed as a coarse halftone screen of the colorant and the sample being printed as a tint of the colorant in a normal mode of operating the printer.