public Puzzle(Form1 form1)
{
    buttons = new Button[3, 3] { { form1.button1, form1.button2, form1.button3 },
                                 { form1.button4, form1.button5, form1.button6 },
                                 { form1.button7, form1.button8, form1.button9 } };
    //button reference from form1
}
public void reset()
{
   //reset all the colors of buttons in the puzzle to lime
}

public void FlipCells(int row, int col)
{
   //when certain button is clicked(this event is done in the form1.cs), say for (0,0) change color of cell (0,0),///(0,1) and (1,0) by calling changeColor method
}

public void changeColor(int row, int col)
{
    //test current color of the cell, and change it
}