Fresco painting in the ancient world was buon fresco, which means painting on a thin layer of fresh, wet lime plaster. The process involved laying down a layer of plaster, waiting an hour, then painting. Fresco painters would have had seven to eight hours to complete their work, until the plaster became too dry to work any longer; the plaster would be completely dry within twelve hours.
The process of mixing pigments with wet plaster would have fixed the colors and made the fresco more durable; had the Mycenaeans and Minoans worked a secco, or on dry plaster, their paintings probably would not have survived. However, it was this same chemical process of mixing pigments with the alkaline plaster that limited the color palette. This is why you see only reds, yellows, blues, whites, and blacks in Mycenaean and Minoan frescoes.