They kinda look alike just with a diferent shades of the same color

Possible. Their names and color schemes are pretty matching. Not to mention their cutie marks.
I can see them being siblings or close relatives.
Just remember that MLP fanbase can be pretty... hardcore.
The Incest community will really take this to a whole NEW level.

7506795
I knew one fan-artist whose headcanon was that they were cousins.

7506795
...they roughly do look like they could be siblings, but then the question of why are they in separate schools comes into play.

7507029
That's pretty much the biggest argument against them being siblings - why would parents send one kid to an elite prep school, and send the other to a decidedly plainer one, and its rival at that? It's not unheard of for parents to send their kids to two different schools (my parents, for example, enrolled me and my brother in different schools during grade school), but there's usually some mitigating circumstance involved (both schools were part of the same public school system, and my brother's special needs).

I could see them being cousins of some sort, perhaps even distantly related to the point that they aren't even aware of it, but brother and sister? I doubt it.