Modified theme colors map can not change color of some components

Created by: ysds

From my comment: https://github.com/twbs/bootstrap/issues/27712#issuecomment-444167717.

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;