Modern artists often build a palette based on the three primaries of "color theory", but that is just one way to build a palette. Renaissance artists used a four color palette: red, yellow, green and blue. The 'Velazquz palette', an even older palette used for centuries uses just three colors: yellow ochre, burnt sienna and ultramarine blue.
Once the value study was done I thought about the palette for the painting. I wanted a three color palette that would capture the warmth of the scene as well as provide colors similar to what is seen in the photograph. The blue pigment I used for the value sketch matched the sky colors very closely. I then selected Yellow Ochre, not the yellow in either my warm or cool color wheel, but a close match for both the float and the sea oats. For the final color I selected a vibrant red. You can see the primary colors (blue, red and yellow) and three secondaries (purple, orange and green) made form mixing the primaries to right of the sketch.