The artist's palette: whatever working surface or object might be chosen as a support for squirting out paints. I use a "butcher's tray"---the metal enameled meat tray used, yes, by butchers---as my watercolor palette. It's perfectly smooth, it never stains, it's easy to wash off in the sink whenever necessary. And it's basically indestructible. My first butcher tray palette was smaller and a bit simpler in shape than the one I show here, with a nice black rim around the upper edge. I still have that tray-palette, and use it for projects that require only a few colors. The tray I show in the photo is a later model---larger, giving more room for mixing.
The artist's palette is also the actual array of paints used in painting. For watercolors, I use only Winsor & Newton Artist Water Colours. As with my brushes (http://thewendywatsonblog.blogspot.com/2013/09/my-brushes.html) these watercolors are among the most expensive one can buy. But they are worth the cost. A tiny bit goes a long, long way---one small tube lasts me for years, if I am careful to keep it tightly capped so it doesn't dry out. (And actually even if it has dried out, it can still be resuscitated and used normally with a wet brush.) The quality of the paints, their handling, the intensity of their colors, are always the superb. My palette---array of colors---is relatively small. Many years ago my publisher very graciously made me a series of proofs of all the colors that I had then in my palette---far more than those above. The proof demonstrated to me which colors reproduced faithfully to the original, and which did not. And it explained why some of the reproductions of my illustrations were not satisfying. As a result of this experiment, I very sadly eliminated some of my favorites from my palette because they reproduced so differently from the original: Cadmium Red, Prussian Blue, and others. But the palette with which I was left---the palette which I still use today---is one that I know will consistently reproduce my work and be faithful to it: yellow ochre, raw sienna, cadmium yellow pale, cadmium lemon, brown madder alizarin, light red, burnt sienna, permanent rose, cobalt green, olive green, terre verte, hooker's green, winsor green, cerulean blue, antwerp blue, winsor blue, winsor violet, alizarin crimson, neutral tint, sepia, and black. Unfortunately, some of these colors are no longer manufactured. Fortunately, I stocked up on all of them some time ago, and have enough on hand for years to come.