welcome to the high arts of blending :)
what happens in the first renderer is an alpha blending with the background, which is black in your case. so the color channels get mixed with black where the alpha channel is less than 1.
in the second renderer you are doing the same thing, so it gets even darker.
you have two options depending on how and when you want to modify the color channels, either disable alpha blending in the first renderer, or disable it in the second renderer: