Use a Color Expression node () to add coloring (according to an expression that you define) to the shapes or lines defined by a plot. You can add this subnode to the following plot types: Line Graph, Point Graph, Global, Nyquist, Arrow Volume, Arrow Surface, Arrow Line, Contour, Isosurface, Particle Trajectories, Point Trajectories, Ray Trajectories, Streamline, Admittance Graph, Impedance Graph, Reflection Graph, Spot Diagram, Waterfall, Whirl.

In the Model Builder, add and define a plot group. Right-click the plot node (for example, Streamline) and select Color Expression.

For Color Expression subnodes under arrow plot nodes, you can choose Arrow length from the Color data list to color the arrows according to the arrow length. The default setting is Expression, and then you can enter an expression for the color in the Expression field below.