The bootstrap 3.4 customization website does
not
provide
a preview for color values (ridiculous). This bookmarklet
will inject a script that adds a reactive previews for color values. It works with variables and
the following functions: lighten, darken, saturate, desaturate, spin.
fade, fadein and fadeout are currently not supported.
Clicking the bookmarklet anywhere other than on the customization page will redirect you to the customization page. Clicking the bookmarklet on the customization page will ask you whether you want to download and run the script on the page. If you click cancel, nothing will happen.
You can find the source code for the bookmarklet here.