I'm making a pasta with kale pesto (kale, olive oil, pine nuts, garlic, pecorino), but I want to make the pesto a day ahead. Will it turn brown like basil pesto?
If you cover the pesto with some oil, it should seal off the pesto and keep it from browning.
I also learned from Alton Brown that quickly blanching basil will keep the bright green color and pesto would not turn brown. Might work with kale too.
In my experience, kale doesn't oxidize nearly as quickly as basil--which oxidizes almost instantly without exposure to heat (blanching) or acid (lemon juice.) Yes, you can safely make kale pesto a day ahead without it turning brown. I'd probably add a little lemon juice anyway, but if you cover it well it'll be fine.
Pestos made from alternative greens (i.e. Other than basil) tend to stay green much longer. It should be fine for several days.