So, the use of colors and abstractions isn't exactly anachronistic. Here is a painting done in France in 1906.
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However, I don't think they're going for "this could have been painted in the 1920s." It is very similar to the type of modern artwork for NOLA, Jazz, and Black history. See here:
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So, isn't that anachronistic to Frontierland or the 1920s?
Not if this area of Frontierland becomes New Orleans Square similar to Disneyland.
A modern mural in the style of NOLA murals depicting the Jazz greats of the the past (Luis the crocodilian) does 'fit.'