I’ve gone for Citizen’s first watch with a black coated case today – this model was launched in 1970 and mine is from March of that year. Using the 7290 movement, with 23 jewels and second setting (‘hacking’) this model was offered with two colour schemes, and this is the monochrome version. The case number is 4-720083. The alloy case is 30% lighter than stainless steel, and Citizen described the coating as more resistant to wear than stainless steel. The dial is very easy to read, with its raised hour markers and clearly contrasting hand set:

I featured the other dial variant as a featured watch, but please note that it has incorrect hour and minute hands and day wheel, and the wrong case back – it was an early purchase, before I got better informed 🙂  With more info, it’s here: https://sweep-hand.org/2012/03/07/this-weeks-featured-watch-25-the-custom-v2-blackie/