I've heard the words 'Canvas' and 'Pallette' used about authors, when someone is trying to describe an author's style or technique. 

Think about Tolkien.  His world, where his fantasy takes place is essentially Middle Earth.  (It's not a planet, it's essentially an enormous flat world, consisting of a single great continent, and some islands far away, to the 'west', the Grey Havens.  You can't go around Middle Earth and come back to where you were; and nobody really tries.)

This is Tolkien's canvas.  His whole story lives on this canvas, and in a sense he manages to convey the greatness, the dimensions of it, and we never feel cramped in it. 

But recall that his action takes place on this canvas, this stage, over several generations.  There are the elder gods, and they have their adventures, which have consequences centuries later.  So his canvas extends N, S, E and W, but also back in time.  If his stories extend over many eons, his Canvas would be considered to be proportionate larger.  So the concept of a canvas is a necessary tool when talking about epic fiction.  I don't know much about these matters; I'm just guessing. 

Another word they use about an author is his (or her) pallette.  The pallette an artist (a painter, to be precise) uses, is the set of colors he uses.  Some artists use all the colors they need, mixing and blending and shading until they get the exact hue they require.   Other artists, intentionally restrict themselves to a very few colors, though they do mix those colors among themselves.  In modern art, I think I see this trend towards a minimalist pallette. 

The word pallette is used in a different sense to 'Canvas'; it is talking about the tools the author uses, the shades of meaning she uses, the particular brush-strokes she uses, whether—and how—she mobilizes the experiences of her audience, the stories in the news, the mythology that we see in the Bible, all as the raw material of her story and her character drawing.

I don't mean to imply that an enormous canvas, and a huge pallette make an author effective.  I myself use a modest (read small) canvas; my stories are not at all epic; they're little intimate things.  Even Galactic Voyager has a small canvas, because of the very few people involved.  Alexandra has a bigger canvas, but not much bigger.  And I have to admit that my pallette is small, because (despite being a 'published' author,) I have little or no training.

But my modesty is enormous, as anyone can see! 

Kay