Missing navbar link bg colors

While I was modifying my own custom navbar I successfully changed all the colors only through variables:
```scss
$navbar-default-bg: rgba(0, 0, 0, 0);
$navbar-default-link-color: $-firstColor;
$navbar-default-link-active-bg: $-secondColor-blured8;
$navbar-default-link-active-color: $-thirdColor;
$navbar-default-link-hover-bg: $-secondColor-blured8;
$navbar-default-link-hover-color: $-thirdColor;
```
Then when I wanted my dropdown to have transparent background instead of white I had to add this:
```sass
navbar-default .navbar-nav > .open > a
  background-color: transparent
```
But, suddenly this background-color is on the top overriding other backgrounds and creating some unexpected behavior. So, I though instead of adding more css rule sets all over the place I asked myself why _navbar.sass doesn't include `$navbar-default-link-bg` color ?

This way everything would be simpler by using only variables.

Do you think these 2 variables `navbar-default/inverse-link-bg` should exist in _navbar.sass ?

Thanks.