"Flow Visualization: Used in fluid dynamics testing or leak detection, especially in lab simulations or field testing.
Fracture Tracing in Hydraulic Fracturing: Colored particles (often polymer-based) can be pumped into fractures to track proppant placement or fracture geometry.
Tracer-based Diagnostics: Some colorful or fluorescent materials are used as chemical or particulate tracers in well diagnostics or reservoir modeling. "