Hi ook -
What you are experiencing is typical and can be very easily corrected by increasing the intensity of you skylight (assuming that you sphere reflection actor is set to an intensity of 1). You will need to play with the exact value base don your individual level, but you can get 99.9% close. You can never get to 100% because of how the SSRs are generated in the rendering process, but you will be able to get the color variation gone completely and if you provide any sort of breakup in light, or texture, the SSR line will be unnoticeable to your player.
The Gif does not do a great job of color representing it looks much better in the engine itself.
Thank You for your question -
Eric Ketchum