Mixing oils or acrylic colours/shades?

I see purple mixed with yellow. This mixture gives you a neutral gray. Make a few mixtures with more yellow/less yellow and use the cooler mixture for shadow area, warmer for sunlit area.

Try to avoid using black paint - it's such a dead colour. if you want a deep shadow tone, mix red & green or orange and blue together instead.

Use a dry brush for the stone texture - squeeze most of the paint out of the brush and drag the brush on its side across the surface so it deposits paint only on the textured surface of the paper, letting the colour beneath show through.

have fun!

The texture you should be able to get with your brush strokes. For your color, I'd mix up what you used for the lighter parts, then add just a touch of black to make it grey.

just try real hard,as my art teacher says,if you need it to be exactly the way it is then tack a pic. of it.