Since you're having a problem with magenta, check that magenta is valid, then try printing it out:

 
#!/usr/bin/perl -l

use strict;
use warnings;
use Term::ANSIColor qw(colorvalid);
use Term::ANSIScreen qw/:color :constants/;

my $valid = colorvalid ('magenta');
print "Color string is ", $valid ? "valid" : "invalid";
print MAGENTA  . "Magenta" . RESET;
[download]

See:

Term::ANSIColor
Term::ANSIScreen

Additional tests:

ansicolor
colortest

To run ansicolor:

cat ansicolor
[download]

colortest prints out all 256 xterm colors.