I decided on natural coloring for the finished illustration. I did try the dark purple/bright orange combo and liked it. However, I will keep it for another style of illustration. It's decidedly more sinister. This version makes a nice mate to the sea horses. I am also keen to illustrate the blue ringed octopus. I still don't want to be submerged with octopi, but I might visit the aquarium soon to see them in person.
Edit: The ad currently displayed below this is for the Intous tablet I use. How do they know?