我有一个具有以下架构的文档集合：

{ 
    "_id" : ObjectId("8dcaac2eb104c2133d66f144"),"Shape" : "circle","Color" : "blue" 
},

我的目标是为一系列文档动态获取特定字段的值。对3个文档的Color值的请求的响应应如下所示：

{
    "blue"
    "green"
    "yellow"
}

我正在使用Mongodb和nodejs，这是我的代码：

var field = req.params.field
var field_option = {};
field_option[field] = 1;

db.collection.find({_id: {$gte: first,$lt: last}},field_option).toArray(function(err,data){
    if(err || !data) throw err;
    res.json(data);
});

但是，输出错误：

[
    {
        "_id": "8dcaac2eb104c2133d66f144","Color" : "blue" 
    },{
        "_id": "8dcaac2eb104c2133d66f145","Shape" : "square","Color" : "green" 
    },{
        "_id": "8dcaac2eb104c2133d66f146","Shape" : "triangle","Color" : "yellow" 
    }

]