“In the real world there’s no such thing as a white piece of paper. Even if the paper was a perfect diffuse reflector with no flaws, the colour is still determined by the lighting. You won’t get a perfect light source that will give you a perfect distribution of chromatically perfect light across your perfect diffuse piece of paper. So in ArtRage we add some chaos to the creative process with a rendered light source across imperfect paper.” — AndyRage
ArtRage is known for giving you that natural painting look. And since it’s a painting tool, it seeks to mimic what you would see in the real world of painting by giving you a specialized Canvas with grain and lightning.
If you’re like me and want a pure white canvas (for digital sketching), here’s what you do: Menu [View] –> Canvas Settings and you’ll get a box that looks like that (I’m using version 5). Uncheck “Canvas Lightning.” That’s it. Click on the Canvas Color and change it to white because by default it’s not 100% pure white. When the lightning is off you can choose any color for your Canvas and it’ll be flat.