Dryadella zebrina leaf color question

[Paul Mc]

First off, what color should the leaves be? I did not take very much notice of what the color was when I got them, but they are currently a bit darker than a lime green. The main reason I'm asking though is because it has two new leaves that have a lime yellow coloration to them.

Is this a sign of too much water or light, or perhaps a sign of not enough light?