How to declare a constructor that has default parameter?

How do I write a constructor that can take in a default parameter? Do I declare the default parameter when declaring private data members or inside the constructor itself?

    Color class:
    private:
        int red;
        int blue;
        int green;
    public: 
        Color(int r, int b, int g) {red = r; blue = b; green = g;}

    Table class: 
    private: 
        double weight;
        double height;
        double width;
        double length;
        Color green;
    public: 
        Table(double input_weight, double input_height, double input_width, 
double input_length, Color green = green(0, 0, 60)){
        weight = input_weight; 
        height = input_height; 
        width = input_width; 
        length = input_length;
    }

I would like to be able to write a constructor that takes a default parameter. But I don't know how to write one (The above Table constructor is the one I'm having problems with). I would like to have an object Table that has different weights, heights, widths, lengths, but all tables will be green. Thanks for the help!