Painting and drawing with the Art Media tools : Using the Marker tool
 
Using the Marker tool
The Marker tool lets you apply pigment that resembles drawing with a marker on a canvas. Marker pens are a slightly wet medium, though generally not wet enough to interact with other wet media. The pigment goes on the canvas with a multiply function, simulating the interaction of using a pen repeatedly on the same spot. Pens generally have a very sharp fall-off at the stroke edge, and there is full canvas penetration even at light pressure.
Marker tool options
Edit workspace 
Marker tool options include
Shape — defines the shape of the marker tip
Size — defines the size of the tool head in pixels
Thickness — defines the aspect ratio of the tool head
Rotation — defines the angle of head rotation in degrees
Head Tracking — controls whether the tool head bends around the path of the stroke, or whether it remains at a fixed angle
Trace check box — allows the Marker tool to select the pigment color by sampling the data below the center of the tool, regardless of the layer type
Important! When you hold down the mouse button to begin the stroke, note that a single sample is performed and the resulting color is used for the duration of the stroke.