The challenge of neutralizing yellow:
Yellow at full strength is still a light value. It is therefore a challenge to turn it from the light into shadow without it being overpowered by other pigments. I grayed the yellow with a mixture of ultramarine blue and alizarin crimson after having made a page of color swatches using both a cool yellow (lemon) and a warmer yellow (cadmium yellow pale). The best neutrals were created when the violet I mixed to gray the cool yellow leaned more toward the alizarin (warm) and the violet I mixed to gray the warm yellow leaned more toward the ultramarine (cool). All of the swatches are useful. Sometimes you might want the yellow to lean toward green or toward orange, but not so far that it loses its yellow identity.
My scanner read the cadmium yellow pale more as an orange. I adjusted the color, trying to make it a bit truer to the swatches.