This post is about the colours.
I have lots of colours, but I usually use the same few. My core colours for oils are: Phthalo Blue, Lemon Yellow, Rose Madder and Titanium White. This collection of colours may be minimal, but they are very flexible; many of the paintings on this blog were completed using them, sometimes with a supplementary colour or two.
These colours are shown - on a wooden palette - above right.
I find that greens - notoriously difficult to mix - are readily achievable with these colours - usually all four. Natural greens often tend towards brown, so the Rose Madder is essential.
I painted Grey Wethers and Black Bullocks (rght) entirely with these four colours.
Elsewhere, I frequently use Burnt Umber and Ultramarine as subsidiary colours. Mixed together, these last two make a good, quick dark (a lot quicker than mixing a similar shade from Phthalo Blue, Lemon Yellow and Rose Madder). If you add white to this dark, you get a nice range of greys.
I don't, generally, use black... unless I'm painting LEGO figures.
Then there were the poppies. It is possible to get a fairly bright red by adding Lemon Yellow to Rose Madder, but it is an awful lot easier to use Cadmium Red.