The most likely reason your Rhoeo Oyster is fading is due to a lack of light. Your plant prefers bright indirect to bright light. If placed in an area where it can receive a couple hours of direct sunlight, the colors will become more vibrant. If it is placed in a lower light environment, its coloring will fade.
If you suspect your plant is fading because of it’s access to light, take a look at your space and find a sunnier spot. A window sill or sunny shelf is perfect for your Rhoeo Oyster to show off its gorgeous colorful leaves.