Yellow ochre is one of the earliest used colors and is still one of the most useful on the palette, indispensable for making skin tones. Permanent bright and transparent yellows eluded artists for millennia despite the clear need.The many poor offerings included obsolete colors like Orpiment and Massicot, mostly very impermanent. Since the mid 19th century there have been the excellent cadmium’s which offer indispensable opaque yellows from pale light yellows to deep orange tinged golden shades. Since 1910 various organic transparent yellows have been marketed under such terms as Hansa and Arylide but they usually are not so permanent as the cadmium’s. If I had to choose just one yellow for my Palette it would be a toss up between Yellow Ochre and Cadmium Yellow Light. I think I would go with the cadmium simply because it can in mixtures make the widest range of colors.