Kulay dugo ang gabi

Sorry to demystify the cinematography but it was a question of COST. Color film stock was prohibitively expensive then and the producers couldn't afford to shoot all the scenes in color. This practice was prevalent in the Philippine film industry in the late 60's/early 70's. I remember a billboard advertising a comedy as "filmed in partly color"(sic). If the visual inconsistencies tended to enhance the narrative and add to the creepy character of the movie, well and good. So, there it is--another mystery gone.

Incidentally, it is not widely known that Gerry De Leon was an MD but never practiced this profession. His family was in the movie business and he promptly went into it after graduating from med school.