Which version of less is this compatible with?

I am trying to use a feature that is present in less.js V3.5.0 ([Maps](http://lesscss.org/features/#maps-feature)) but it throws an error.
Consider the following less:
```
@colors: {
@red: {
base: #f00;
};
@blue: {
base: #0f0;
}
};

@theme: blue;

.color(@color, @type) {

}
.test {
color: @colors[@@theme][base];
}
```
This should produce the following output:
```
.test {
color: #0f0;
}
```

Instead I get an error saying
`Undefined Variable: @colors[@@theme][base]`