in link properties and link trigger indicator properties ZZZZZZ can be entered as a colour hex code.

"administration -> general -> trigger displaying options" does validate input.
here the error message is "Colour is not correct: expecting hexadecimal colour code (6 symbols)."

when attempting to enter ZZZZZZ for custom graph item or bar report, error message is :
Warning. Field [color] is not a colour

all colour fields in zabbix should apply proper validation.

and, please, do not reimplement it for each page anew, let's use a single function/validation mechanism