Sass customization fails tab-bar color on Android

I customized the tab-bar color as follows:

$tabs-dark-bg:                   #333333 !default;
$tabs-dark-border:               $positive  !default;
$tabs-dark-text:                 #fff !default;

This works fine on iOS:

but fails on Android:

And the main-layout.html has:

<ion-tabs class="tabs-icon-only tabs-dark">
 ....
</ion-tabs>

Why isn’t Android picking up on the color?

Thanks