If your blue sky washes move into your sunrises turning the sky green, here are some helpful tips. Watercolor is painted in layers that are usually transparent and much blending of color is done in washes and glazes. This presents a problem when painting skies that you wish to remain clear of green.
To avoid greens, yellow ochre should be mixed with titanium white to give it less of a tendency to turn green. Yellow ochre’s properties (e.g., lightfastness, opacity, staining, granulation) vary greatly depending on the manufacturer and pigments used.
1. Use a mixture of yellow ochre that has pigments PW6 and PBr24…this means titanium white with yellow ochre. (Note: Some yellow ochres may contain a synthetic pigment PY43.) First lay down the yellow ochre then gently layer in the blue. Practice layering using light pressure, a soft brush, and not too little nor too much water. Instead of green, you will see a warm blue gray. Let these air dry. I mix M. Graham yellow ochre and titanium white watercolors to get pure colors without too much cost, and without forsaking quality. If you want to use just one tube, Winsor Newton’s yellow ochre watercolor contains both pigments.
2. Keep white between both yellow and blue. Use masking fluid (remove with rubbing) or use gum Arabic (wipe off with a little water and towel) to keep the colors separated. The remaining white line can become part of the art looking like clouds. You can also use water after the paint has dried to let the colors gently meet, being careful to not produce green.
3. Place a light wash of pink and/or orange between blue and yellow, as seen in a sunset.
4. Use a hard-edge technique to keep the colors from mixing. However, the full painting should contain lots of hard-edge shapes for continuity purposes.