I call this set my "Six Pack": Titanium white, ivory black, Venetian red, yellow ochre, cobalt blue, and raw umber.
The emphasis in this painting is on the warm sky and the cool shadows on the near side. I didn't use black on this one. The darks are made with cobalt blue, Venetian red and raw umber.
Darks often have more character if they're made up of loose mixtures of warm and cool colors.
The main reason for the black is for painting in grisaille. There's no better way to learn about a new painting medium than to paint a still life using nothing but black and white.
Because the Six Pack doesn't have high-chroma reds and yellows, it automatically gives you a slightly faded, old world feeling, like the color of memories.
It also doesn't let you mix strong greens, which can be a good thing. Instead, it forces you to interpret the scene in terms of simple warm/cool oppositions.
You can see this focus on warm vs. cool in the work of classic British landscapists like J.M.W Turner, David Roberts, and Richard Parkes Bonington.
Here's a video showing how I work out the sky and background first, then the smaller verticals, and finally the delicate wires, using a graphite pencil over the dry paint.
The Jack Richeson company, who makes the only artist-grade casein I know of, liked my Six Pack idea, and they asked if they could offer it as a set.
Gurney's Casein 6 Pack:
Titanium white, ivory black, Venetian red, yellow ochre, cobalt blue, and raw umber.
Gurney's Casein 6 Pack with Brush Set
Amazon offers the six-color set with a portable set of synthetic brushes in a travel holder.
I also suggested a wider assortment of colors if you want to start off with a fuller gamut.
Gurney's Casein Explorers Pack contains: titanium white, ivory black, alizarin crimson, cadmium red scarlet, cad yellow light, cad yellow medium, cerulean blue, ultramarine blue deep, chrome oxide green, burnt sienna, raw sienna, raw umber.
This set is non-overlapping except for the commonly used colors white, black and raw umber. That way you can start with either one and expand to the other.