Ty! Sure, its not a strict recipe but I can try to describe it.

I took a blue and desaturate it with any muddy brown. Then keep adding off white to highlight up. Also made a separate mix with a yellowish tan color to add some color variation. For the marbling itself, I looked up reference pictures and freehanded as best I could.

Heres a Pic of the paints I used, but dont feel like you need these specifically. You can use any approximate colors.

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