I made my second smoothie today, which was really a variation on the first one. All the ingredients were the same except: I used 3 kale leaves and 3 collard leaves, instead of the handfuls of romaine and spinach. I also added a starfruit, and I used a lot more lemon juice. I read somewhere that lemon juice cuts down the bitterness of the greens.
It was still kind of bitter, but I enjoyed it! Next time, I'm going to use either one or two types of greens, instead of three!