3-color terminal symbol set

Recently I was playing with image to terminal ANSI art conversion. There are some nice symbols that allow to more precisely describe an area shape. There are some more common ones, and some not supported yet on many platforms and many fonts.

But regardless, all those symbols are limited to only two colors: foreground and background. And that cannot be changed. However there is a way to synthetically create a third color by dithering fg and bg colors.