Yellow and black mixed together make green. So, yes, you're right, the yellowish varnish made it look green over the black fiber carbon.

You can use the varnish but put a tape line along the fiber carbon edge. To protect the epoxy over the hull, find a clear coating and i'm sure others can recommend a brand.

As far as an area that didn't wet out totally which is a white area there's no magic easy fix. If you sand down to the wood, you can just create a mess. I have taken artist oil paint and mix a color to match the surrounding wood and paint it with that and blend it in on the edges. Once dry, varnish over it.