So the middle picture shows my initial sketch in pale lemon yellow. Because I don't use a pencil sketch for the Koi paintings, I still need to map out the positioning of the fish on the page, so I do a very pale wash to indicate the composition. The next step in the first picture on the left is to build up the colour on the fish. From my analysis of my reference photo, I found that the fish had blue and purple running through it as well as the dark orange splotchy scale pattern and a white head. I haven't used too may different layers, as I wanted the bright colours to be very pure and stark against the white head and later the pale green pond.
After the fish have completely dried (a couple of hours), I have painted in the watery background - first by wetting the background with plain water with a large brush, then dabbing the colour (Pthalo Green, Ultramarine Blue and Paynes Grey) onto the water which makes the colour run and disperse, then adding the cling film onto the wet background and scrunching it into a pattern and leaving it to dry completely. The pattern it creates denotes a watery background.
This original is for sale here or the print of this painting is available here.