Turning off Design that is applied

I've been using slides from the Content Library and it's great to jump start a course but I've gotten myself in trouble trying to change the design. I've created a whole training and 1 slide had a white background that I think was being applied by one of these Design options, at least it had a box around it on the tool bar. I wanted to great rid of the white background because I had applied a gradient fill background to the other slides and I want it to match. I clicked on the design option hoping that it would turn it off and instead it change my whole course applying different colors all over the place. 

How do you turn off a Design setup and is there anyway to get back to the color scheme I had created. I change colors on most things to match a particulate palette. I also can't figure out when you look at the available color palette, how it's deciding what colors to apply when. Any help understanding that would be appreciated