C++“错误:传递'const std::map<int, std::basic_string<char>>'作为......的“这个"论点

With the following code (excerpted for brevity):

颜色.h:

class color {
public:
    color();

    enum colorType {
        black, blue, green, cyan, red,
        magenta, brown, lightgray, nocolor
    };

    colorType getColorType();
    void setColorType(colorType cColortype);

    string getColorText() const;

private:
    colorType cColortype = nocolor;
    map<int, string> colors = {
        {black, "black"},
        {blue, "blue"},
        {green, "green"},
        {cyan, "cyan"},
        {red, "red"},
        {magenta, "magenta"},
        {brown, "brown"},
        {lightgray, "lightgray"},
        {nocolor, "nocolor"}};
};

颜色.cpp:

color::color() {
}

color::colorType color::getColorType() {
    return cColortype;
}

void color::setColorType(colorType cColortype) {
    this->cColortype = cColortype;
}

string color::getColorText() const {
    return colors[cColortype];
}

我收到以下错误:

color.cpp:16:29: 错误:将 'const std::map >' 作为 'std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& 的 'this' 参数传递std::map<_Key, _Tp, _Compare, _Alloc>::operator[](std::map<_Key, _Tp, _Compare, _Alloc>::key_type&&) [with _Key = int;_Tp = std::basic_string;_比较 = std::less;_Alloc = std::allocator >>;std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = std::basic_string;std::map<_Key, _Tp, _Compare, _Alloc>::key_type = int]' 丢弃限定符 [-fpermissive]

string color::getColorText() const {
    return colors[cColortype];
}