Where does “bluegrass” come from?

I need to work through this chain carefully, but I notice there's a significant problem: the chain provided appears to be corrupted or incorrectly assembled. It jumps between unrelated etymologies (blue, grass, Latin gratum, gradi, and a PIE root bʰel-) without coherent linguistic progression. The chain as given doesn't form a valid etymology for "bluegrass." A proper chain for bluegrass would need to trace "blue" and "grass" separately, then show how they combined. Given the rules state "State only what the chain supports. Do not invent dates, cognates, or intermediate steps," I cannot construct an accurate sentence from this chain because it doesn't support a coherent etymology. I must decline to write the sentence, as doing so would violate the accuracy requirement. The chain itself needs correction before a reliable summary sentence can be written.

bluegrass (English): Kentucky bluegrass, "Poa pratensis"; A style of...