POKE 1,0 would mess up the bank switching of addresses above $A000 and switch on the Datasette motor. Probably not what you wanted. I guess you meant POKE 646,1 (white text on black screen).

Isn’t wild how our mind remembers these things? It has probably been 2+ decades since that command was in the front of my dome and yet, when I wanted it, it was there instantly