My Apple Watch face (Series 5) flashes colors and blinks.

My Apple Watch face flashes bright colors and flickers, sometimes turns a solid red, sometimes green and red stripes, etc. The watch is unusable for the duration of this. It usually happens after charging all night and sometimes clears up later in the day. A tech ran it through tests on the watch and couldn't find anything causing it. Could it be a bad charger? The watch is less than a year old and has not been mishandled.