On early television stations, what typically filled the screen from around 11pm until 6am? test dummies test patterns tests testing colors

I'd say test patterns.

Also known as a test card, a test pattern is a television test signal that was sometimes broadcasted when the transmitter was active but no program was being displayed on the screens. It was usually used since the earliest TV broadcast and is currently, often used for calibration, alignment and troubleshooting the downstream signal path. The purpose of the test pattern transmission back then was to enable engineers install or repair TV receivers.

i will say b. laboratory technician   and if wrong then sorry

power left de cliffs or inoonsw