The tool beneath the Chalk tool is the "Color Picker" tool. With it selected you can move your mouse/pen over a color on the canvas that you may have mixed and select that color for use. Alternatively, if you are painting with another tool, you can hold down the "ALT" key on your keyboard and click over the color as a short cut. One thing about having the tool selected though, is that the option to pick up the "lighting" is there for you to toggle on or off. The 3d lighting on the canvas may change the color from a light blue to a dark blue depending on it's location on the screen. Also, with the lighting on, if you try to pick up the color from a thickly laid down oil brush mark, the color picker may pull up the dark shadow, or bright highlights behind one of the raised strokes, instead of the color itself.
As for splatter or splotches, my best guess would be to use stencils. ArtRage itself doesn't have a specific tool for it.
Nothing is easy to the unwilling.