MIL also used to advise me on clothes. To be precise, she thinks my color combinations are too 'Modern'.
Somewhere along the line, she took a seminar about dressing according to 'natural seasons'. Because I am a 'Winter Person', my strong colors should be navy blue or dark green. I should wear lots of white and my accent colors should be light green and baby blue. On no account should I ever wear anything smacking of red, yellow or orange. Forget about purple.
She hasn't pulled this up in a while but it was a real bone of contention for several years.
It was especially annoying since my own mother refused to let me wear any colors other than blue and white until I was seven. Even black or brown shoes were verboten.