Usotsuki Majo To Haiiro No Niji summary:

"Everything looks the same in this ashen world. Flowers, birds, rainbows, myself. I wonder what 'color' we are. If I meet a witch, will I be able to see 'colors' too?"This story takes place in a world that has lost its "color". Only "witches" can see them. One day, Luma, a boy who longs for a vibrant world, heads to a forest where witches are said to live. After getting lost, he meets a witch named Ilya, and their encounter changes the fate of their "colorless" world.An adaptation of the light novel of the same name, which was written by Soraru and illustrated by Tsukasa Kiryuu.