When is it "Bad Luck" to wear a color on St. Patrick's Day?

 When the color is

ORANGE,

since that is the color 

associated in N. Ireland

with

Protestantism / Unionism;

even so the two colors

GREEN

and

ORANGE

are linked together

on the Irish flag.

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Originally the "color" for

St. Patrick was BLUE

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best tip:

stick to - - - GREEN & WHITE ---