"Use Nodes" Needs to be (En/ Dis) -abled?
I'm not sure what the issue is with my Blender 2.81.16, but I had to click on the Use Nodes bar and collapse/ hide all of the options in order for the change in Base Color to actually work:
I had to click on the blue Use Nodes bar ....
,,, to close out most of the options. Only then would changing the Base Color take effect.