The green mark you refer to is not a reference mark for the tightness of the oil filter cap when reassembling it after an oil change. The green dot is a production mark put there by the engine builder who assembled the oil filter. It is an inspection mark to show the cap has been properly torqued during assembly. When reassembled after an oil change the marks don't necessarily need to line up. Get the proper filter cap wrench and you will have no problem removing it.
It is a right-hand thread and unscrews counter-clockwise.