How to save?

i have made a windows form.In that form i have three button RED, GREEN, PINK
when i click RED the form color goes PINK
when i click GREEN the form color goes GREEN
when i click PINK the form color goes PINK.

the problem is suppose user click  PINK then form color goes pink but when the user open the same form again its comes to it default color.I want code to save the user setting.

plz help me [email protected]