It sounds like you've made the canvas transparent, and what you're seeing is a pattern behind the canvas.
It's easy enough to make the canvas opaque again.
At the bottom centre of the ArtRage window is the small preview pane.
In the bottom right corner of the preview pane is a small triangle. Click that to bring up the options menu.
Select 'Edit Paper Settings' near the bottom of the menu.
Near the bottom of the paper settings you'll see six dials. One of those dials is labelled 'Opacity'. Click on the dial track and drag around to make the value 100%.
That will make the paper totally opaque again.
Click 'Ok' to keep the paper settings.
Your painting should be back against your normal canvas.
Note that you can change the colour and texture of your canvas from that dialog box as well, if you want to experiment with different things.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"