Here's a script that changes the bgcolor(fullscreen) to black and text color to bold green

It does no such thing. This code (your posted code):

#!/usr/bin/perl

use strict;
use warnings;

# change bgcolor and text
system("echo -e"\e[1;32;40m black");

sleep 5;

# revert to original color
system("echo -e "\e[0m");
[download]

doesn't even compile

When posting untested code, please mark it as such.

When posting tested code, please post the code that you actually ran.

Shame on you. You should know better.