A:Answer I believe that is the ARGB LED; however, you can verify by going to the below links to reference your build on the MSI website. I didn't use the ARGB LED even though my motherboard supported the connection. I was happy with the standard LED lighting that was offered as I am not a big fan of LED lighting. If you use the ARGB LED, you will need to download software to utilize its features.
Links for MPG GUNGNIR 100 case to assist with your build:
Manual - https://download.msi.com/archive/mnu_exe/pc/7G09-manual.pdf
Quick Guide - https://www.msi.com/PC-case/support/MPG-GUNGNIR-100#down-quickguide