What does it mean for a block to be colored red in the mergeset?

A block colored red in the mergeset is one that does not contribute to Kaspa's main consensus chain. Kaspa's GHOSTDAG protocol assigns each block a color — blue blocks are the ones that count toward consensus calculations, while red blocks are structurally present in the DAG but excluded from those calculations. A block can be a parent of another block (meaning it helped build the DAG's shape) and still end up red, which means its work does not feed into metrics like blue score or blue work. Understanding this matters because it explains why Kaspa's security and finality calculations depend on the mergeset specifically, not simply on how many blocks exist in the graph.