Perform simple desaturation or grayscale conversion of RGBA colors.
desaturate(color, gamma_correct = FALSE)rgba color strings
logical, whether to apply non-linear gamma correction. First performs gamma expansion, then applies the gray-scale channel weigths, then gamma compression.
rgba color strings, the grayscale colors. The information from one of the three rgb channels would be enough. The alpha value is not touched.
see https://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
Other color functions:
alphablend()