The only consolation was that I am presently obsessed with John Singer Sergeant and I recalled this, which I found on this site
“There are stories of Sargent wearing out the carpet as he dashed backward and forward from his easel; of sudden expletives as he wrestled with the problems of representation: ‘Demons, demons!’ he would cry out in frustration; of scraping-downs and rubbings-out as he abandoned what he had begun and started again.
It has been good for me to brood on this, for people always assume that beautiful paintings materialise from the end of a brush as if by magic - I am just as bad - and that if they do not it must mean you haven't got what it takes (whatever that is). I try to remember it is hard for everyone and that persistence and patience are required.
More in despair than hope, I decided to have another go with a different palette. I ditched the chromatic blacks, the burnt umber and ultramarine mixes that were failing to produce anything except the colours of decayed swamp, and re-laid my palette with Rembrandt Transparent Oxide Brown (a colour that seems to "behave itself" so much better than Burnt Umber), Rembrandt Cadmium Yellow Deep and Gamblin Warm White.
I looked very closely at the reference photo taken by Janina Suuronen on Paint My Photo and exaggerated the merest hint of orange that I could see in the horse's coat - the red arrows mark the spots:
I appreciate it is a bit of a jump from Janina's photo to my painting, but that is how I did it.