how can i ve a region from a maskcolor:

i ve painted a usercontrol with several things including magenta some parts of the control wich i want to be transparent.
i ve a function from VB6 that i made that will trace the region for 1 color, but i dont know how to get a function like Point or GetPixel in VB .NET, so i can know the color that is mask!!

plz somebody help me...