Human Physiology- Why are polychromatic and orthochromatic erythroblasts are named so?

Chromatic refers to colour. Polychromatic erythroblasts are called so because their cytoplasm has a variable colour, so it can be of many (poly) colours. Orthochromatic erythroblasts are the ones that have their cytoplasm the same (orto) colour than erythrocytes.