My critiques:
Main XN: too many different and unnecessary blues.
XN-G: Too bright! Tone it down a bit. Also a mite sexist, if G stands for girl.
XN: black and orange text disappear against some of the gray backgrounds, as do the dark gray post controls over their bluish-gray fields (but I actually like that). This one is the easiest on my eyes.
As my rule of thumb, for every bright, saturated color not including white there should be two neutrals.
General critiques:
-Space allotted to username, icon, etc. is too wide. Just empty space doing nothing but being distracting.
-"What's New" button at the top is redundant (alternatively, the link to "New posts" can be removed in favor of the button)
I would highly recommend looking at colorschemedesigner.com to generate sets of colors that (scientifically) work together.
What I would think is interesting to try is creating a color scheme based on an Xterra: charcoal gray, silver, primary color as background (one for each known paint color), bits of amber and red (perhaps as "clicked link" colors) to represent lights.