Make sure your succulent soil is well-drained to prevent waterlogging. No direct sunlight. Snake plants do not need any direct sunlight, as mentioned. Sunlight, as well as the cold weather, bring out the dark colors of the plant. It may become whiter if the plant isn’t allowed to rest in shade or protected from direct sunlight. It's fine to trim roots if they are beginning to rot. If you are unable to see any change, use q-tips and a soft toothbrush with soap to remove the fungal spots. If needed, consider using grow lights to provide enough light indoors.