transparetn images

i tried to make one color of my image (in a picturebox) transparent. But the only thing I manage to do is making one color the same color as my form. For this I used some code i found in the msdn-libraries:

' Assumes a picture has been assigned to the BackgroundImage property.
Dim g As New System.Drawing.Bitmap(Button1.BackGroundImage)
g.MakeTransparent(System.Drawing.Color.White)
Button1.BackgroundImage = g

I adjusted the code so it would be useful to an image in a picturebox but it isn't realy transparent, it gets the collor of the form it's on

i didn't have this problem in VB6

Is there someone who could help me?