Help! Connecting Macbook Pro (2013) to external monitor

I have a 2013 Macbook Pro Retina 13', and I'm trying to get it connected to an external monitor. Trying to use this system closed display mode.

However, when Macbook is closed, and I play a video in full screen mode on my monitor (Youtube, Netflix), the display goes purple and green. I am using Mini display cable in my Macbook thunderbolt 2 port, connected to HDMI port on the monitor. The video and audio works great on my monitor, except when I play a video in full screen mode with my Mac closed.

Here's what I know so far:

• It's not the monitor, because the 2018 Macbook Pro with USB-C cable doesn't have this fullscreen video problem.
• When my macbook is open, full screen video works fine, no purple/green. But I would like to use closed-display mode to work.
• I made sure my cable connection was not loose.
• Macbook is connected to power source during closed display mode
• Just updated my software and still have the problem.
• Might be a cable problem, but I also tried using HDMI-HDMI cable and still have the same problem.

Anyone else had this problem/know how to fix it? Thanks!