first_list = ['Johnny', 'Steve', 'Ben', 'Johnny']
cursor = favoriteColors.aggregate([{'$match': {'name': {'$in': first_list}}
    }, {'$project': {'part': {'$map': {'input': first_list, 'as': 'inp',
    'in': {'$cond': [{'$eq': ['$$inp', '$name']}, '$color', None]}}}}}, {
    '$group': {'_id': None, 'data': {'$push': '$part'}}}])
Iterating over a dictionary to create a list