Basil is always a bad boy for me with it's tendency to turn brown.
This is probably not the flavor profile you are looking for, but the green chile adobo in More Mexican Everyday is a brilliant green, stays that way (in the fridge, my jar is a little over 2 weeks old) and would be lovely on fish.
It calls for half a head of garlic and 4-5 serrano chiles that are both dry roasted and peeled, a big bunch each of cilantro and parsley, a cup of olive oil and 2 t salt, all whizzed in the blender.
Let me see if I can find a picture.
Edited to add: You can see the jar in this photo on the breakfast thread. And here it is stirred into some rice and beans with shrimp.
