Small error with Color in class

[Rhap]

//// point.h
using namespace System::Drawing;


class point
{
protected:
int x;
int y;
Color col;

public:
point();
};

////cpoint.cpp
#include "stdafx.h"
#include "point.h"

point::point()
{
x = 0;
y = 0;
col = Color::Blue;

}

///Error
c:\...\point.h(9) : error C3265: cannot declare a managed 'col' in an unmanaged 'point'
1> the value type may not contain members of managed types

So this is for a class assignment, and the Class point was basically handed to us as a starting point. Everything compiled without errors until I created the .cpp file. I'm almost sure it's a missing namespace or include, but i don't know which one. Help would be appreciated!