Can you post pictures? What is the name of the quartz? More information will help folks give better suggestions.

Hard to say without pictures but if you're scared of dark gray just go for a medium to light gray. It will still compliment the gray in the stone without being too dark.

This is the dark grey backsplash with the quartz

This is the model home. It has lighter gray back splash but with granite.

I think that dark gray would work well. And since it's glass it will reflect more light than a ceramic. But wait for everything to be installed before making your final backsplash decision.

I have to decide today as it’s part of the builder’s order :(
So your thoughts are with the lighter gray?

Thank you Sina for your prompt reply. I was in a hurry when I was replying earlier! What makes me hesitant about the dark gray backsplash is that it might be too dark so it will frame the kitchen and makes it look smaller! My other concern would this affect my furniture selections to be very modern? My main living room is facing the kitchen.

One more question? Should backsplash reach up to the end of cabinets in the area where the hood is located? Or it can only go up to where the vent starts?

I would go for the light gray, but I have fairly conservative tastes. How far the tile goes is a matter of taste; you'll see photos of both ways. I'd say it depends on the vent hood. If it is visually substantial -- completely fills the space horizontally, say -- then I'd say that's where it should stop. If it's thinner, or the horizontal part is clear, take the tile up higher so you don't create a visual break where there doesn't need to be one.

Thank you Mother of Giants :) You totally have a point in regards of the vent.
What are your thoughts about having the backsplash only in the area of the hood and leave the rest of the kitchen without or maybe use something else?! I am afraid the subway tiles will go out of style and I would be stuck with it as it’s already gonna cost me almost $3600

Something like this!

As you found, there are beautiful ways to do just what you describe. :) I think most people go with the more attention-grabbing tile above the stove and simpler (and less expensive) tile everywhere else. That usually means subway tile ends up in the "everywhere else" category, but obviously there are different sorts of subway tile and just about any tile will draw more attention than plain wall.

Bassankardy what type of quartz is that? Beautiful!

Do you really have to choose your backsplash now? Ideally it's chosen after everything else is done. Could you get a credit from the builder instead, and then have it done at a later time on your own??
If you are really forced to pick now, better to go very simple. You're MUCH less likely to regret it than something busy, elaborate, or "interesting" that perhaps doesn't work so well with the rest of the room.

I'll add that I share your concern about subway tile becoming dated, though I think that will first hit the ubiquitous "plain white subway tile." I've wondered if 15 years from now 3×6 in a brick pattern will inspire the same reaction as 4×4 installed on a diagonal, but if you like it, then why worry about it? I'd certainly rather get something I like that may become dated in a decade than something I don't enjoy that is on the cutting edge of decor.