Is there a way to paint dithered in GIMP? Indexed mode will make existing gradients dithered, but using the brush tool or airbrush tool after dithering will just make a solid color, instead of just dithering what should be gradients around the brush.
Paint with a cloning tool. Have a dithered texture as the source. The dithered texture can be as well random grain as some algorihmic looking repeating pattern.
You can also have a full layer of dithered texture. Paint to its layer mask.
Reverse it. Have a dithered pattern in the layer mask and paint normally. That allows fast color changing, but the colors in the same layer have the same dithering pattern. The following sample is made this way. There are different layers and patterns for green and red.
As the 4th way I suggest to paint as normally. Then insert just over it a layer of dithered texture that simulates mid grey with 2 different greys (not full black and white). Give to that layer blending mode = hard light.
None of these methods unfortunately can directly dither R, G and B by using a recognizable sized pattern to produce the wanted dithered RGB color.