angular.js: $q parallel set

gistfile1.js

var fields = {};

var p1 = $http.get('/api/field/sizes').success(function(sizes){
    fields.sizes = sizes;
});

var p2 = $http.get('/api/field/colors').success(function(colors){
    fields.colors = colors;
});

$q.all(p1, p2).then(function(){
    // How do I have 'fields' populated here?
    console.log(JSON.stringify(fields)); // returns '{}'
});