Pretty sure Highlight came first. Both originated or passed through the URW organization. Highlight preceded their bankruptcy and Blacklight appeared after they emerged from bankruptcy.
URW, for those not familiar with their history, was pretty much the inventor of digital type and sold their Icarus font creation system to most of the foundries back in the 1980's. They were also the contractor for font digitizing for ITC for many years. I would make an educated guess that Blacklight is legal due to the name change and URW having created the vectors for Highlight in the first place.