That is why the trees, which are darker than the blend layer's blue color, do not show through the blend range. Notice how the colors, in the sky, that are nearer or the same lightness value as the blend range's blue color are subtracted leaving a a very dark near black value. Lets take a look at another example. In the above example the trees being darker in lightness than the Blend layer's color do not show through the Blend color. The sky colors of the landscape are closer in lightness to the Blend color and are beginning to show through the Blend color.
Lets take a look.
Blend color Blend results Notice how, in the above example, the trees are now beginning to show through the Blend range. Not only are some of the colors in the trees lighter than the Blend color, the colors in the sky and grass are lighter, so the Blend color over those lighter underlying colors have less opacity. You can further alter the opacity values of the difference Blend Mode by adjusting the Blend Range opacity ramps. Lets take a look at a couple of examples. These examples use the blue colored blend layer.