"I saw that it wasn’t the black that made the picture come alive but the light reflected on the black surfaces... The light was... coming from the color that is the greatest absence of light."

Said Pierre Soulages, quoted in "Pierre Soulages, Leading French Abstract Painter, Dies at 102 Once called 'the world’s greatest living artist,' Mr. Soulages was best known for exploring the possibilities of the color black" (NYT).

 For more than four decades, Mr. Soulages worked every possible variation on black in an evolving series of paintings he called “outrenoir,” or “beyond black,” sometimes using spoons or small rakes to create new textures in his thick slabs of paint and evoke subtle effects of color and light.

“Some mornings, it is a silvery gray,” he told the critic Bernard Ceysson in 1979. “Sometimes, capturing the light reflected from the sea, it is blue. At other times it can be tinged a coppery brown. In fact, it always corresponds to the light that falls on it. One day, I even saw it green: There had been a storm, and there was a blaze of sun on the trees not far away.”

Imagine spending 4 decades painting in black paint. Not black shapes on white, but all black, with the variations in brushstrokes and texture.

And then he is "commissioned to make 104 windows for the Romanesque abbey church of Sainte-Foy in Conques." This is 11th century architecture. What do you do?

Rather than design stained-glass windows, he devised a series of translucent panes, framed by black steel bars, whose variable thickness diffused and modulated the incoming light. The windows were installed in 1994.

Here's a documentary. Go to 38:35 to get to the church windows: