“…I had ranged the reds from pink to orange, which rose into the yellows as far as lemon with light and dark greens.”
— Vincent van Gogh writing to Theo about painting a portrait of Roulin?s wife, 22 January 1889
What I take from this is to not think of a colour as limited to only tubes marked that colour, but to include analogous colours too (colours that sit alongside one another on the colour wheel). So, not thinking of red as reds alone, but including yellow and orange as well as purple and blue. For blue to include green and yellow. Yellow to include green and orange, and so on.
Or put another way, the ‘secret’ to Van Gogh’s beautiful reds is to use more than only red.
Last year  I painted almost nothing but flowers to accustom myself to a colour other than grey, that’s to say pink, soft or bright green, light blue, violet, yellow, orange, fine red. And when I painted landscape in Asnières this summer I saw more colour in it than before.”
Looking at the daffodils in the sunshine this spring, all the different yellows, I’ve found myself thinking about that quote attributed to Picasso about “they’ll sell you thousands of greens but never the particular green you’re after”. The yellows of the same daffodil change as the sun shifts, as the light falls on different parts, as shadows move, blooms open and fade.
To paint them I feel as if I need to dig out every yellow, blue and green I’ve got along with some reds and oranges. The temptation will be procrastinating into colour mixing. The way around this is to mix on the canvas not my palette. I may still get distracted by colour, but can all form part of a layer in a painting.
Vincent van Gogh’s various paintings of cut sunflowers in a vase (e.g. Sunflowers 1888) are probably his best-known flower paintings, but he also painted growing flowers, such as these irises. I enjoy not only his use of colour and mark making, but the way he makes flowers fill the whole composition and flattens the depth of field (an influence from Japanese art on him). A floral colour field, to apply a concept from a few decades later, and another influence on my painting, Rothko.