I like them all, but have to agree about the blue as well. Typically you should see other colors such as yellows and reds as well.
What lens did you use?
Looks like it could be CA, and, the star trails are exaggerating it.
As for having any landscape in the images, that completely up to you. But for most astrophotography you want to avoid it and only capture the sky.
With that said, when I shoot wide field star trail or star scape images I'll have some trees in there. Partly because I have no choice where I live, and I also use those same star trail frames for time lapse animations, and, the trees give the animation more dimension and depth when you can watch the stars move behind the trees. However, I will aim the camera high enough so I don't have man made structures such as my house or my neighbors. That's also to aim higher than most of the sky glow.