Last tip I suggested that you try tinting your boards. A warm mid-tone colour.
This eliminates the need to cover the stark white when painting in oils. I use a mixture of titanium white and burnt sienna.
This tip I want to suggest an alternative colour. Try a darker blue/purple. If you have a close look at the picture of Lake Wanaka, you can see that the background was painted in a pink colour and the other with a mixture of ultramarine blue and burnt sienna and crimson.
Lots of this colour appears all over the painting very deliberately. Not only does this technique eliminate the problem of covering the white board, but it also helps to bind the whole paint together into a common "Atmosphere".
|Lake Wanaka, NZ|
If you try to mix the back ground colour in acrylic and let it thoroughly dry, then re-mix it in oil colour. Use this colour as your atmospheric colour. Tint every colour that you mix for that painting. The whole painting will have a distinct tint towards that original colour.Now try a different colour! A hot colour or a cold colour! I have had the best results when I have chosen my subjects well. (i.e.: A hot colour for a sunset, a cold colour for a cold scene).
Also keep colour on the dark side. A strong colour is fun. If you look closely at the Wanaka painting, you will see what I mean.