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