Explain the node status colours in KNIME.

Red means the node is not configured, yellow means it is configured and ready to run, and green means it has executed and holds output data.

The practical value is diagnosis: in a workflow of forty nodes, the colours tell you instantly where execution stopped.

Worth adding that red does not necessarily mean an error — a newly added node is red because it has not been opened yet. It is a problem when a previously green node turns red, which usually means a column it referenced was renamed or removed upstream.