"A touch of red"

If you saw the movie Mr Turner you probably remember him adding a blob of red to a painting. (This is what that was about.)

Not this much, though

When you look at almost any painting by Constable, you'll see a bit of red ... put your thumb over it to "remove" it, and something vital is missing.

Hadleigh Castle (via)

The White Horse (via)

In Julia Caprara's embroidery classes I learned that a touch of red - or turquoise, her favourite - both draws your eye and sends it to other parts of the work.

By Julia Caprara (via)

What "touches" do you use to enliven your work?