I would suggest that, referencing on existing pixels/other people's pixels on HOW to shade. But when pixeling details, it is best to have a real thing as reference. Sometimes, other people's pixel's works due to various reasons, they use more than 6 shades, they use different palette, they have more contrasting shades, different scales...

Unless you are creating a new type of leaf, It would be better to look at the real stuff in real world.
Currently, I am undecided on what that leaf WANT to be.