How to use a brush over an image in c# so that the background appears highlighted

Question

We have an image and are using Graphics. We want to overlay a rectangle on an image and make it appear highlighted in Yellow (or some other color). What we have done is create rectangle and fill it with a brush. We could use a solid brush and turn down the opacity but it appears muddy. We believe that we could use a gradient brush and use a blend mode to create the highlight.

We want to do something similar to this ( https://www.graphicsmill.com/docs/gm/blending-modes.htm#Multiply ) in c# with the Microsoft library. Does such a thing exist?

Any help would be appreciated.