As my colleague Jen explained, the class you have set for your content blocks is custom made and we cannot attempt to modify what we do not see or what we do not know how its made. In this video I have recorded my steps in modifying a single block of content.
As far as the tile widget - you need to specify your criteria for it. I would recommend to open a support ticket where we can help you solve the problem faster.
I am using Sitefinity 8.0, created a template from scratch dropped an image and content block on the template. No theme is selected. Opened the advanced edit on both widgets, changed the background color to #8F0000.
There are no color changes. This is Sitefinity 8.0, no other pages. Just a basic setup.