Fix color selection for airbrush

[AshrayShetty4]

When the foreground color is changed in the document (selected from the color palette), the color doesn't automatically update. Instead, you have to change the airbrush pattern(select a different spray size) to make the change in color happen. The issue is that I can't move the color change "function" into any of the canvas event handlers (just doesn't show anything).

[AshrayShetty4]

Note: One more thing that I noticed is that now when the color switch happens, the previous color still persists. On multiple color switches, gives a brown/black color.