picture box background after activate

i have a simple project with 1 form that has a picturebox. its color in its properties is green. i want to change the color to black by putting in form_activated the following

Dim gu As Graphics
gu = PictureBox1.CreateGraphics

gu.Clear(Color.Black)

and it doesn't do it! color is green when the form is displayed. if however i put a breakpt in the form_activated routine it stops at the breakpoint and then when the form is displayed the pw is black.

what indeed is going on.

and how can i use the graphics routines in the activate subroutine?

thank you

follys