use Term::ANSIColor qw(:constants color);

$line = "<b><font color=blue>blue and bold</font>bold but not blue</b>neither blue nor bold<font color=red>red but not bold</font>";
@colors = (); # colors stack

for (split /(<[^>]+>)/, $line) {
    if (/^<([^\/>][^>]*)>$/) { # opening tag
        if ($1 eq 'b') { # bold
            print color 'bold';
            push @colors, 'bold';
        } elsif (/\s+color="?(\w+)"?/) { # font color
            print color $1;
            push @colors, $1;
        }
    } elsif (/^<(\/[^>]+)>$/) { #closing tag
        pop @colors;
        print color 'reset';
        for $color (@colors) {
            print color $color;
        }
    } else { # regular string
        print "$_\n" if ($_);
    }
}