I recently installed a hallmark. Greenish-yellow is ground. As long as you don't have a 115 volt pump, and supposing the pump is one of their 230 volt labeled models, the blue wire connects to one hot leg (red) and the black connects to the other hot leg (black) but it doesn't matter which. Just keep greenish to green. Its kinda yellow but more green. Mine had a sticker on the yellow-green wire that said PE with a ground symbol on it. I guess PE is their codename for Planet Earth.
also, you are correct. The wires coming from the pump are 16 gauge at best. Super thin. I installed my pump in the fall of 2020. I will be very surprised if it lasts a year. The online reviews of these Hallmark pumps are love/hate. Some folks say they are great and others say they aren't worth the package they were shipped in. Time will tell.