bootstrap/scss/root required, this variables uses in many files.

The whole bg-, text- update in 5.1.0 has seemingly complicated the entire process of adding a new theme-color. The only way I could find to get the bg- and text- classes regenerated for the new "custom" theme color is....

@import "functions";
@import "variables";
@import "mixins";

$custom: #df711b;

$custom-theme-colors: (
  "custom": $custom
);

$theme-colors: map-merge($theme-colors, $custom-theme-colors);
$theme-colors-rgb: map-loop($theme-colors, to-rgb, "$value");
$utilities-colors: map-merge($utilities-colors, $theme-colors-rgb);
$utilities-text-colors: map-loop($utilities-colors, rgba-css-var, "$key", "text");
$utilities-bg-colors: map-loop($utilities-colors, rgba-css-var, "$key", "bg");

@import "bootstrap";

I discovered this on an SO question and here's the working code demo

Whereas in 5.0.2 one could simply follow the example in the docs...

@import "functions";
@import "variables";
@import "mixins";

$custom-colors: (
  "custom-color": #df711b
);

$theme-colors: map-merge($theme-colors, $custom-colors);

In addition to that, the suggested way of extending color utility classes generates HEX color values instead of RGBA and still keeps useless --bs-text-opacity: 1; in every custom color class

The whole bg-, text- update in 5.1.0 has seemingly complicated the entire process of adding a new theme-color. The only way I could find to get the bg- and text- classes regenerated for the new "custom" theme color is....

@import "functions";
@import "variables";
@import "mixins";

Thanks!
This really needs to be written in the official documentation!

I consider this either a regression or a lack in documentation.
Thanks @iatek for the above! Unfortunately it didn't work for me.
What finally worked for me was moving mixins after the merge-map and map-loop, like this:

// CUSTOM COLOURS
@import './variables';

// Configuration
@import "node_modules/bootstrap/scss/functions";
@import "node_modules/bootstrap/scss/variables";

$theme-colors: map-merge($theme-colors, $custom-colours);
$theme-colors-rgb: map-loop($theme-colors, to-rgb, "$value");
$utilities-colors: map-merge($utilities-colors, $theme-colors-rgb);
$utilities-text-colors: map-loop($utilities-colors, rgba-css-var, "$key", "text");
$utilities-bg-colors: map-loop($utilities-colors, rgba-css-var, "$key", "bg");

@import "node_modules/bootstrap/scss/mixins";
@import "node_modules/bootstrap/scss/utilities";
// ... and the rest of boostrap

Oh, and btw the same is true if you need to add spacing classes:

@import "node_modules/bootstrap/scss/functions";
@import "node_modules/bootstrap/scss/variables";

// Extend the spacings
$spacers: map-merge(
  $spacers, (
    6: ($spacer * 6)
  )
);

arrrggghhhh add +1 to frustration of note. this change has had me tearing my hair out.

i sort of got it working with

_variables.scss (my custom variables)

@import "../../../../../node_modules/bootstrap/scss/functions";
@import "../../../../../node_modules/bootstrap/scss/variables";
@import "../../../../../node_modules/bootstrap/scss/mixins";

$colors: (
...
);
$theme-colors: (
...
);
$theme-colors-rgb: map-loop($theme-colors, to-rgb, "$value");
$utilities-colors: map-merge($utilities-colors, $theme-colors-rgb);
$utilities-text-colors: map-loop($utilities-colors, rgba-css-var, "$key", "text");
$utilities-bg-colors: map-loop($utilities-colors, rgba-css-var, "$key", "bg");

....

styles.scss (main style)

@import "./variables";
@import "../../../../../node_modules/bootstrap/scss/bootstrap.scss";
...

at the devs, its changes like this that might actually drive people away tho. would suggest you consider "ability and ease of extending bootstrap" as a core just like getting the code working right. i know people might disagree with this, but this change for instance has some what had me questioning if bootstrap and me remain in a loving relationship or not). 12k lines of css :( last i looked it was around 8 or so

Sorry we've been slow to investigate and identify a path forward. We'll need a little more time to experiment and validate the issues identified here. Definitely not in our interest to be causing headaches for folks :).

Hehe thanks mdo. I think the 5.1 update took a few people by surprise. Some "breaking" things like this but on the face of it it looks like 5.0 but it's still a big update.