This layer is a neutral wash over the canvas. It like carpet underlay creating a basic background tone and colour.

If you don’t want to faff around waiting for things to dry use acrylics which dry really quickly. You can put oils over acrylics but not the other way around so acrylics can be a fast way covering the white canvas.

I made a dull olive layer with yellow ochre and a dab of phthalocyanine blue. I watered the paints down and applied with a paint brush, it’s so thin it didn’t leave brush strokes and allowed the drawing to still show through as can be seen in the next step.