I read this solution on TechRadar, check and see if it helps
If you find that your Mac's display starts randomly showing rainbow colors when turned on, especially when it comes to displayign drop shadows in the system UI, then you will need to perform a SMC reset:
SMC Reset for the iMac
1. Shut down the device
2. Disconnect the power cord from the monitor
3. Wait 60 seconds
4. Reconnect power cord
SMC Reset for MacBooks with internal batteries
1. Shut down the device
2. Plug in the power adapter
3. Hold down Shift + Control + Option on the keyboard, as well as the Power button at the same time.
4. Release the keys and the light on the power adapter will change color briefly.
5. Boot your MacBook normally
link to the full article is here:
http://www.techradar.com/how-to/computing/macos-sierra-problems-here-s-how-to-fi x-the-most-common-issues-1329043