Basics: Viewport display: solid color

I have a heck of a time KEEPING the simple, object-by-object color option engaged – I had it at one point, but then must have hit a button somewhere or changed modes or something

Here’s a screenie: I “believe”, for what that’s worth, that I’ve got all the appropriate tools engaged, but the Object in question isn’t displaying in color. The frustration is that it WAS working a bit ago. I am able to get the Material color to appear, but not the Object color.

You are using Workbench as render engine.
That means that settings, you are modifying, are settings for Rendered Display mode.

Settings in Render Tab -> Render Display mode, F12 render .
Settings in ViewPort Shading Popover -> Solid Display mode.

The fact that you use Workbench as Render Engine does not modify that behavior.
There are 2 places showing same parameters but that does not mean that they are setting same thing.