[RMMV] TYPE ERROR WHEN TESTING THE GAME?

Hey everyone I am getting this strange error when I test my game, I have tried everything I could think of I am stumped this has never happened to me before.

https://rpgmaker.net/media/content/users/60230/locker/2019_10_17_14_50_40_816x652.png

I tried and it says something to do with the background color?