Styling twitter bootstrap buttons

I found the simplest way is to put this in your overrides. Sorry for my unimaginative color choice

Bootstrap 4-Alpha SASS

.my-btn {
  //@include button-variant($btn-primary-color, $btn-primary-bg, $btn-primary-border);
  @include button-variant(red, white, blue);
}

Bootstrap 4 Alpha SASS Example

Bootstrap 3 LESS

.my-btn {
  //.button-variant(@btn-primary-color; @btn-primary-bg; @btn-primary-border);
  .button-variant(red; white; blue);
}

Bootstrap 3 LESS Example

Bootstrap 3 SASS

.my-btn {
  //@include button-variant($btn-primary-color, $btn-primary-bg, $btn-primary-border);
  @include button-variant(red, white, blue);
}

Bootstrap 3 SASS Example

Bootstrap 2.3 LESS

.btn-primary {
  //.buttonBackground(@btnBackground, @btnBackgroundHighlight, @grayDark, 0 1px 1px rgba(255,255,255,.75));
  .buttonBackground(red, white);
}

Bootstrap 2.3 LESS Example

Bootstrap 2.3 SASS

.btn-primary {
  //@include buttonBackground($btnPrimaryBackground, $btnPrimaryBackgroundHighlight); 
  @include buttonBackground(red, white); 
}

It will take care of the hover/actives for you

From the comments, if you want to lighten the button instead of darken when using black (or just want to inverse) you need to extend the class a bit further like so:

Bootstrap 3 SASS Ligthen

.my-btn {
  // @include button-variant($btn-primary-color, $btn-primary-bg, $btn-primary-border);
  $color: #fff;
  $background: #000;
  $border: #333;
  @include button-variant($color, $background, $border);
  // override the default darkening with lightening
  &:hover,
  &:focus,
  &.focus,
  &:active,
  &.active,
  .open > &.dropdown-toggle {
    color: $color;
    background-color: lighten($background, 20%); //10% default
    border-color: lighten($border, 22%); // 12% default
  }
}

Bootstrap 3 SASS Lighten Example