What do blue and red blocks mean in Kaspa's GHOSTDAG?

GHOSTDAG assigns every block a color — blue or red — to decide which blocks actively contribute to network consensus. In Kaspa's blockDAG, many blocks can be created in parallel at the same time. To keep the network in agreement, GHOSTDAG processes a set of candidate blocks called the mergeset and labels each one: blue blocks count toward consensus and help confirm transactions, while red blocks are still valid — not discarded — but do not contribute to consensus. This coloring system is how Kaspa maintains consistent agreement across all nodes even when blocks arrive simultaneously, which is the heart of what makes a blockDAG different from a traditional chain.