Change form background

Question

I would like to change a forms background from another form.

I have form1 and form2 in my application, on form2 i have a combobox with the options.
Whan i select a color in the combobox, i want form1's backcolor to change and not form2's.

I used this code:

Form1 form = new Form1();
form.BackColor = Properties.Settings1.Default.Black;

But it doesn't work?

The same thing happens when i try to change form1's opicity!