color warning in _root.scss on heroku deploy

[m5o]

scss/_root.scss is generate this warning for each iteration of $colors.
Example from a heroku deploy output.

remote:        Using sass 3.5.2
remote:        Using sass-rails 5.0.6
…
remote:        W, [2017-12-14T15:26:15.622115 #401]  WARN -- : WARNING on line 4, column 7 of /tmp/build_7b[…]3/vendor/bundle/ruby/2.4.0/gems/bootstrap-4.0.0.beta2/assets/stylesheets/bootstrap/_root.scss:
remote:        You probably don't mean to use the color value `blue' in interpolation here.
remote:        It may end up represented as #0000ff, which will likely produce invalid CSS.
remote:        Always quote color names when using them as strings (for example, "blue").
remote:        If you really want to use the color value here, use `"" + $color'.
remote:        W, [2017-12-14T15:26:15.622271 #401]  WARN -- : WARNING on line 4, column 7 of /tmp/build_7b[…]3/vendor/bundle/ruby/2.4.0/gems/bootstrap-4.0.0.beta2/assets/stylesheets/bootstrap/_root.scss:
remote:        You probably don't mean to use the color value `indigo' in interpolation here.
remote:        It may end up represented as #4b0082, which will likely produce invalid CSS.
remote:        Always quote color names when using them as strings (for example, "indigo").
remote:        If you really want to use the color value here, use `"" + $color'.
…

Reference

🔗 twbs/bootstrap#24354
🔗 twbs/bootstrap#24549 (comment) – possible fix

[m5o]

🔗 twbs/bootstrap#24549 (comment) - possible fix

🔔 @glebm Is the fix useful?

[glebm]

@m5o Does this warning also happen on Sass v3.5.4?

[m5o]

@m5o Does this warning also happen on Sass v3.5.4?

Couldn't get it reproduced with v3.5.4 on a heroku deploy

In a different project of mine, it's still present… ok found the issue.
The project variables didn't catch up latest syntax:

-$colors: () !default;
-$colors: map-merge((
-  blue:         $blue,
-  indigo:       $indigo,
-  purple:       $purple,
-  pink:         $pink,
-  red:          $red,
[…]
+$colors: () !default;
+$colors: map-merge((
+  "blue":         $blue,
+  "indigo":       $indigo,
+  "purple":       $purple,
+  "pink":         $pink,
[…]

Sorry, my mistake! Problem solved ☑️