难题啊对于这个"类"

//大家帮我看一下怎样用string来给这个矩形输出颜色（例如：输出red）
#include<iostream.h>
#include<string>
class Rectangle
{
public:
    double GetWidth();
    double GetLength();
    double GetArea();
    double GetPerimeter();
    void SetWidth(double myWidth);
    void SetLength(double myLength);
private:
    double length;
    double width;
};
double Rectangle::GetWidth()
{
    return width;
}
double Rectangle::GetLength()
{
    return length;
}
double Rectangle::GetArea()
{   
    return width*length;
}
double Rectangle::GetPerimeter()
{
    return 2*(width+length);
}
void  Rectangle::SetWidth(double myWidth)
{
   if(myWidth>0)
       width=myWidth;
}
void  Rectangle::SetLength(double myLength)
{
    if(myLength>0)
        length=myLength;
}
void main()
{
    Rectangle t1;
    double n,m;
    cout<<"please input width and length:\n";
    cin>>n;
    cin>>m;
    t1.SetWidth(n);
    t1.SetLength(m);
    t1.GetArea();
    t1.GetPerimeter();
    cout<<"width="<<t1.GetWidth()<<"\n"<<"length="<<t1.GetLength()<<"\n";
    cout<<"Area="<<t1.GetArea()<<"\n"<<"Perimeter="<<t1.GetPerimeter()<<"\n";
}