s6 went mono

A strange occurrence happened yesterday with my Galaxy s6 from T-mobile. It is stock, unrooted, and on latest release. all of a sudden, the display screen went into monochrome (black and white ) mode. Battery was at 44%, so i dont think it was due to power saving. I also connected charger to further charge it. After some minutes, i turned it off, and restarted. While restarting, i can see samsung logo in color, and lockscreen was in color for few seconds, and then display immediately went mono. after few couple of more reboots, i wiped the cache in hope to clear any issue due to any app update. but still the same result. Then switched from Nova launcher to Touchwiz , but still the same even after one more reboot. So, i thought the phone may have become defective. Then , after a while, just pressed home button few times trying to unlock the phone, and this time, the screen came back to color!!!!

Has any one ever experienced this? What could be the cause? Software or Hardware?