 <p>In <code>variables.less</code>, the <code>@navbar-default-brand-color</code> variable is used:</p> <pre><code>@navbar-default-brand-color: @navbar-default-link-color; @navbar-default-brand-hover-color: darken(@navbar-default-brand-color, 10%); </code></pre> <p>The error you get is because the darken function (LESS native function) is not able to parse your <code>@my-navbar-link-color</code>, so check you have a valid color (in the snippet, it seems to be valid)</p>