I went through a phase a couple of years ago of toning the background with a thin red and had some success. Red is a good mid-value colour and forces you to pay attention to the darkest darks. Then one or two pieces went horribly wrong and I abandoned the idea.
Here is another go at the same technique. The palette was: cad red medium - for the whole board as a background then the bridle; Alizarin, Prussian Green and a touch of Cerulean Blue - to make those greys in the sky; black, white and a touch of yellow ochre for the shiny bits of tack. A combination of these made the various browns of the horse.
Here is a collage of work-in-progress photos.
Have a lovely weekend everyone and thank you for looking at my paintings.