The Spray Can Tool is useful for subtle shading, blending and producing lines with indistinct edges. Use the Spray Can by clicking once in a particular area of your picture, or by dragging the mouse while holding down the left or right mouse button. Just like a real spray can, the longer you hold the tool over a particular area, the more densely the paint will build up on the picture.

The Option Panel as it appears when the Spray Can Tool is active.

The Flow Rate control on the Option Panel (pictured above) dictates how quickly paint flows from the Spray Can. A slower Flow Rate will give you more control, while a faster rate is better for bold strokes. Like the Paint Brush, the size, edge and shape of the area covered can also be adjusted from the Option Panel.

Setting the Style control to Fade will cause the paint color to gradually shift from Color Box's left color to the right color. (Or, if using the right mouse button, from the right color to the left color.) The speed at which the fade effect occurs depends on the Flow Rate.