In chemistry, orthochromasia is the property of a dye or stain to not change color on binding to a target, as opposed to metachromatic stains which change color. The word is derived from the Greek ortho (correct, upright), and chromatic (color). Toluidine blue is an example of a partially orthochromatic dye, as it stains nucleic acids by its orthochromatic color (blue), but stains mast cell granules in its metachromatic color (red).