The typical grisaille blandness of Netherlandish altarpieces served to highlight the splendid colour inside. The "grisaille" frescoes are painted to look like marble statues that personify Virtues and Vices. There are several different types of underpainting, such as veneda, verdaccio, morellone and grisaille. It is a design or scene in "intaglio" that appears ""en grisaille"" (in gray) tones. In 1953, two grisaille frescoes were discovered on the shorter sides of the room. Below there was a predella of three "grisaille" (monochrome) compartments illustrating the Theological Virtues (1507. The monumental painting of God is executed in grisaille. Niches in the walls contain classical statuary; above the niches are grisaille panels. There are also panels in grisaille (monochrome) showing the Vices and Virtues. With its muted colour tones, it has an affinity to the grisaille painting method. Grey was also frequently used for the drawing of oil paintings, a technique called "grisaille". It is clear that he was acquainted with French grisaille painting. A couple of "grisaille" paintings were uncovered on the staircase, featuring eagle and weapon motifs. Riverside Church's main building contains 51 stained glass windows, excluding smaller grisaille windows. The grisaille beneath would provide the shading, visible through the layers of color.