Hello! Please check out this story by threemorewishes!
LINK: https://www.asianfanfics.com/story/view/1291165

Description | Everyone was born with a soulmate. Someone that they can share love, happiness, sadness and even pain. However, it comes with a catch. When you meet your soulmate, colours start to fade from your vision. Would your love for your soulmate be enough for you to sacrifice seeing in colours for the rest of your life?