Hi Richard,
I think the problem comes in when you start thinking about colors in categorical terms. If you want to group raw umber in the yellow category, then you have to define that category liberally. Looking at raw umber side-by-side with cadmium yellow, they are very different in color, transparency, tinting strength, chemical origin--just about every property. Personally, I don't think of raw umber as a yellow at all. But however you categorize it, it is a relatively neutral earth color.
In the photo below, I mixed some raw umber with white (left). Then I had some fun making "mud" with the primary colors the way we did as kids with poster paint, remember? I mixed cad yellow light, perylene red, and ultramarine blue with white in an attempt to approximate the same neutral shade. I think I came pretty close--maybe if I'd used cobalt blue or cad red light I would have made a more exact match.
Mud comes in many shades of brown/grey-brown/red-brown, etc. So does earth. Raw umber is cooler than, say, burnt umber, so theoretically it has more blue in it than burnt umber. Any relatively neutral color can be made with mixtures of complementary colors. Hope this is of some help in answering your question.
Alex
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