In my diary (whichever version diary I’m using) I colour code all entries.

Red = work (anything work related, desk shifts, meetings, deadlines)

Green = social (dinners out, theatre etc.)

Purple = birthdays

Pink = school (anything study related, assignment dates, exams etc.)

Blue = appointments (doctor, dentist, hair, physio)

Black = everything else (dates bills are due, phone calls to make)

I use the same (or very similar)  colour scheme in Google Calendar also.