Gradient Changing Transition Color

I'm trying to create a gradient fade over a solid color and it is changing the color through the transition. When trying to fade from black to translucent, the transition is gray. Everything I have tried continues to make the fade gray instead of keeping it black and reducing the opacity. I have attached screen shots of what I am experiencing and what I am trying to produce.

How can I keep this from lightening the color through the transition?