For this task, I just decided to go fully freestyle and see what happened.
I chose two contrasting colours for the first one and wanted to see what happened.
I used phthalo green and cad orange to begin with, but I didn’t love the overall effect, so added some cad yellow as highlights.
I then decided to just use the colours I am naturally drawn to and ones I have used to paint backgrounds with before.
Phthalo blue, magenta and dioxazine purple. The light in the photo isn’t great, but in reality, you get this psychedelic underwater effect.