The colors and color adaptation of the European tree frog, Hyla arborea, have been investigated by means of reflectance microspectrophotometry. The results are compared to those previously published on Hyla cinerea.The two species have a number of colors in common (yellow green, light green, green, dark green, black-green, and olive green), while grey colors are assumed only by Hyla arboren and lemon yellow (olive yellow) only by Hyla cinerea. The physical qualities of these colors and the corresponding states of the chromatophores are presented and discussed.