There are a few different ways depending on the look ur going for. Either you can use white and black pastels to mix into the color ur using or you ccan create the allusion of shading by pushing lighter and harder with ur pastel.
the reason he painted space on that painting is because he trying to say that God is one touch away or he's also trying to say we can never feel the famous touch of God
1234 that’s as we’re I’m pretty sure it’s in order already