They are contrary little articles- some days they'll eat carrot, other days they leave them sad'n'shrivelled on the floor .
Darker greens have a higher oxilate (sp) level, increase the likelihood of bladder stones.
I give our pigs about 5-7 different veg for breakfast and supper so they don't get too much of one thing. DH and I are vegetarian s we have the veg anyway
Kale
Spring greens
broccoli (I cut the ends of when I cook for us)
Celery leaves (they don't like the stalks but make sure yo cut them small, they have those strings)
watercress/rocket/spinach mixed salad bags
salad bags but no ice-berg
pak choi/bok choi
romaine
cucumber
small gem lettuce (Sainsburys Red Topped are a favourite
)
sprouts (ours had he remains of a sprout tree for Christmas. GP2 had wind ) 
herbs- our pigs love parsley, GP4 loves mint
pea-shoots
green beans
things-with-leaves (the pigs class as a gree)
carrots with leaves - they ignore regular carrots and scoff the ugly leafed ones
sweetcorn in their leaves
garden leaves , dandelions, (clover but it's high in calcium)
peppers (mine won't eat gren unless there's nothing else)
If we are down to the last day before I go shopping , there's only the green veg/salad , they have a " Scruffy Tea " named after Fernies ScruffyPig who will only eat green 
Scruffy Tea has to be supplemented with fresh ut grass to stop the judgey looks (which is no fun in January, out there with scissors)