RGB+Alpha rendering the color green as white

Sorry there is absolutely no way to tell what you have done to create this problem because we can't see the modified properties of the layers involved, your render settings or anything else. If you rendered using the default Lossless With Alpha and there is nothing funky going on in your composition like guide layers or color corrections then you should get colors. The default Lossless with Alpha is for Premultiplied with alpha color mode and most apps prefer straight alpha but changing this setting would only effect the pixels on the edges. If you comp background color is black the pixels would be a little less gray. If your Comp background color was green the edge pixels would be slightly darker if you put the footage over something with a green background. That setting would have nothing to do with removing the green.