use strict;
use warnings;
use Term::ANSIColor;

my $t = "ACGCGATAGCATTAGACCTGGCACAGT";
my @highlights = (
    # [ start, len, color ]
    [ 20, 5, 'bold blue' ],
    [ 10, 2, 'bold red' ],
    [ 3, 4, 'bold green' ],
);

for my $ar (@highlights) {
    my ($start, $len, $color) = @$ar;
    $t = substr($t, 0, $start-1)                  # first part
       . colored(substr($t,$start,$len), $color)  # colored part
       . substr($t,$start+$len);                  # final part
}

print $t, "\n";