I would go the other way around and define the colors as global variables and set these to be empty in the case where no colors are wanted:

my $red = "\033[31m"; # is there a semicolon missing at the end of the
+ ANSI escape?
if( $ENV{NO_COLOR} || ! -t) {
    $red = "";
}
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See also https://no-color.org and Term::ANSIColor::Conditional.