Use Scss map and map_get to get dynamic variables from map.

input.scss

$white_foo_bar: #FFF;
$map: (
  foo: 'foo',
  bar: 'bar',
  baz: 'white',
  foowhite: 'foowhitecolor'
);


@mixin foo($type) {
  .foo {
    .bar {
      background: $white_foo_bar;
      color: map-get($map, #{$type}white);
    }
  }
}

.div {
  @include foo('foo');
}

output.css

.div .foo .bar {
  background: #FFF;
  color: "foowhitecolor";
}