Ink Art is an earlier version of ArtRage, done for the Microsoft TabletPC experience pack. ArtRage 2.5 is the latest version of ArtRage.
However ArtRage doesn't have a fill tool either...
Instead of using a fill tool to change the background, you can change the paper colour in ArtRage. From the layer menu, choose 'Edit Paper settings', and then change the paper to pure white, or change the paper to transparent and export as a PNG with transparency.
AndyRage's mantra for graphics engine code:
"Sure - how hard can it be?"