I've never tried it, but I wonder if blanching the basil in slightly alkaline water (plus the salt, I guess) might help, with keeping the green color at least. (I don't know about the taste retention). With "the usual vegetables" in E/SE Asian cooking that is a common way to keep them bright green, and it is also done in Western cooking, I believe, in addition to simply blanching them in salted water. But keep the citrus juice out till the end (like just before you use the sauce); acidic conditions *will* generally make green stuff go brown quickly.
Under acidic conditions chlorophyll loses the Mg++ ion and becomes the olive/dark-colored pheophytin. Under alkaline conditions the chlorophyll retains the Mg++ and, at least partly, loses the phytyl & methyl esters (cleavage to the carboxylate moieties, becoming the Mg-chelated analog of chlorophyllin, which has a bright green color).
P.s. the enzyme deactivated by the blanching is chlorophyllase.
