How to overwrite color like mspaint?

I am making a painting Project using a render target.

But Color Combined.
I do not want to mix colors.

I don`t need Magenta, Cyan Color.
just need original color like mspaint.

anybody help?

I modified one of my old projects to show a method of how do that. I erases the previous color by drawing a negative value into the render target. In the material of the brush it has to be set to allow negative emissive values.

there’s a bit of a delay sometimes as the colors switch, I think the value in the render target sometimes gets higher than 1 so it takes longer to erase.

Oh Thank you so much!

I tried, but the color of the part of -1 does not change immediately.

Show here Please, Black Circle

Is there a faster way?

Show here Please, my material function.

// M_Unwrap

// M_3ChannelFinalColor_Test

not sure, if the reason for the delay is that the number are outside the 0-1 range then maybe you could look into the water ripple materials because they somehow return the values to 0 after they are drawn. I think they use two render targets, but not sure exactly how it’s done. I think there’s an example in the content examples project.

thank you!
It has helped a lot!