Modified theme colors map can not change color of some components

[ysds]

From my comment: #27712 (comment).

About a way of changing the theme colors, the document explains as:
https://getbootstrap.com/docs/4.1/getting-started/theming/#modify-map

But, it actually is incorrect after #27378.

demo1: https://codepen.io/fellows3/pen/WYBbEM

$theme-colors: (
  "primary": green
);

demo2: https://codepen.io/fellows3/pen/ZmNYNd

$primary: green;

[MartijnCuppens]

I think we'll need to revert to the state before #27378 to avoid breaking changes.

The way we define colors need to be reviewed at some point because we do not document what the purpose of $primary is in our documentation.

Ref: #23908

[mdo]

I'm okay with reverting that other PR if it solves this problem for now. We can revisit how we use maps/variables with our v5 changes.