I'm not familiar with the trade mark on the back of this palette, but I have had training in fine arts and have used watercolour palettes. This palette was most likely made prior to the 1960's, as modern watercolour palettes from the 1960's on were almost always plastic of some kind, or else enameled metal (the older ones).
The reason is simple: weight. This is especially true for painting outdoors. Even professional artists stopped using porcelain palettes for watercolours once plastic (or later, resin) was available. By the way, I doubt very much that this palette was made for anything other than watercolour work; palettes for oils were -- and still are -- generally made of wood.
These kind of porcelain palettes (particularly the small size you've shown here) were often included in wooden watercolour box kits prior to the 1960's, something that might be given as a Christmas gift. They were also used in "plein air" kits, the compact outdoor watercolour sketching outfits that would fit neatly in a small bag for excursions -- these were very popular. The fact that this is stamped "Made in USA" suggests it is 1950's or earlier. The exact date would be hard to pinpoint, although I'd expect much older palettes (ca. 1900 or prior) would be made in Europe rather than the U.S. Best "guesstimate" of date: 1910's to 1950's. If it was acquired as part of estate miscellany, you might be able to ascribe a closer date based on other items in the lot.
As for value, I think it might have some sentimental or collector's value to someone interested or involved in painting. I could see an artist wanting to perhaps display it as a conversation piece. Clearly it was a manufactured item, and the trade name "Erion" or "Eriom" produces nothing on Google, so I doubt there is much intrinsic value, unlike say, a Tiffany lamp. My suggestion would be to try listing it at about what you would ask for a 1930's to 1950's artisan's tool and see if you get any interest.
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