Avenging Eagle: There a tons of ways to setup blending,
BlendOp can have these settings:
So if you used SUBTRACT then white would get darker and more transparent.
You can also set SrcBlend,DestBlend where Src is what you return from the shader , and Dest is the current pixel in the render target, you have these options:
When its a .fx file you just remove the "D3D11_BLEND_" from the options and insert the rest like "SrcBlend = ONE;".
So there are tons of combinations , the best way is to just try different settings until you find something that looks amazing