Retain RGB values on 0 alpha pixels?

[ReeceGames]

I am making a Minecraft texture pack for bedrock edition, and the grass overlay system puts the overlay color on top of the RGB value of a given pixel, with the transparency of that pixels alpha channel. What this means is, to make a proper texture, you need to put the dirt part of the grass with an alpha of 0.
Unfortunately GIMP replaces the RGB values of a 0 alpha pixel with black.
Does anyone have a way to make a completely transparent pixel that still has a chosen RGB value?

[Ofnuts]

The PNG export dialog has a "Save color values from transparent pixels" option.

In you load this image and use the Pointer dialog, you can check that the colors of transparent pixels are still there. You can easily unerase
by filling the alpha channel with white.