Risk matrix custom visualization
As of release 12.0.3, you can use a risk matrix custom visualization.
Risk matrix is a type of a heat map that shows the probability of a risk event and its impact. It is limited to 4x4 area.
You can find it on GitHub with other custom visualization samples: https://github.com/IBM/ca_customvis/tree/master/code-samples/11.1.x

For more information, see Custom visualizations code samples.