There are a few things I need.

There's a pattern in Photoshop that I'd very much like in GIMP. It's called Guache.
There's also a technique in Photoshop that I'm not sure how to do in GIMP if it's even possible. Color Overlay.

If anyone can help me with this it would be very very very much appreciated. I want to make the sexy oceans I saw here, and the only thing keeping me from doing so in GIMP are those two things.