I recall Grant Fuller spoke about this a lot. From his Youtube channel: The swatch on the right is watercolour Cadmium Orange. He spoke about adding a touch of "yellow" to the Cad Or, though he didn't say which one. He specifically mentioned about creating a combination in the sky that didn't blend to green where the passages mingled. Just an example of a strategy. Blue is CoB toned down a little with the Cad Or. Dark, stormy sky is UB + BS.