In Photoshop, I create a color study, picking colors from my selected gamut directly. I fiddle with the levels slider to create a variation of my first study, which you can see to the right. As much as I like the old-fashioned, faded look of the altered image, I decide to stick to the original, which is more convincingly aquatic.
I spray my sketch with workable fixative and then brush on a thin layer of matte medium to seal the sketch before the painting process. I then begin an acrylic under painting to map out the basic colors of the piece. I tried to do a consecutive wash too quickly on top of my first wash covering the whole paper, which resulted in some of the paint lifting. You can see the results of this as the darker brown border around the edges of the painting. I am not too concerned about this as the background will eventually be covered relatively thickly with paint.
I do a quick, transparent oil under painting using only blue and brown, but the more colorful acrylic layer shows through creating a nice balance. I am pretty happy with the energy in the under painting, so the challenge will be to keep the consecutive layers of oil paint fluid and the colors unmuddied.