Hill of Dreams is pretty dark I remember...
I didn't think so at first, but then I've just reached the bit where he starts to use gorse brushes in an unusual way:
“From a steep and wild hillside, not far from the house, he had cut from time to time five large boughs of spiked and prickly gorse. He had brought them into the house, one by one, and had hidden them in the big box that stood beside his bed. Often he woke up weeping and murmuring to himself the words of one of his songs, and then when he had lit the candle, he would draw out the gorse-boughs, and place them on the floor, and taking off his nightgown, gently lay himself down on the bed of thorns and spines. Lying on his face, with the candle and the book before him, he would softly and tenderly repeat the praises of his dear, dear Annie, and as he turned over page after page, and saw the raised gold of the majuscules glow and flame in the candle-light, he pressed the thorns into his flesh.
At such moments he tasted in all its acute savor the joy of physical pain; and after two or three experiences of such delights he altered his book, making a curious sign in vermilion on the margin of the passages where he was to inflict on himself this sweet torture. Never did he fail to wake at the appointed hour, a strong effort of will broke through all the heaviness of sleep, and he would rise up, joyful though weeping, and reverently set his thorny bed upon the floor, offering his pain with his praise. When he had whispered the last word, and had risen from the ground, his body would be all freckled with drops of blood; he used to view the marks with pride.
Here and there a spine would be left deep in the flesh, and he would pull these out roughly, tearing through the skin. On some nights when he had pressed with more fervor on the thorns his thighs would stream with blood, red beads standing out on the flesh, and trickling down to his feet. He had some difficulty in washing away the bloodstains so as not to leave any traces to attract the attention of the servant; and after a time he returned no more to his bed when his duty had been accomplished. For a coverlet he had a dark rug, a good deal worn, and in this he would wrap his naked bleeding body, and lie down on the hard floor, well content to add an aching rest to the account of his pleasures.
He was covered with scars, and those that healed during the day were torn open afresh at night; the pale olive skin was red with the angry marks of blood, and the graceful form of the young man appeared like the body of a tortured martyr. He grew thinner and thinner every day, for he ate but little; the skin was stretched on the bones of his face, and the black eyes burnt in dark purple hollows. His relations noticed that he was not looking well.”