As Brian said"The mountains being far off would be somewhat greyer and "blurryer" due to atmospheric effects (haze). I think perhaps if you greyed down the mountains and perhaps picked up some highlights in the foreground you would have a fairly accompished piece."
This is called atmospheric perspective . It attempts to mimic the human eye as things in the distance are blurry as apposed to things closer are in focus.
There is nothing wrong with using reference photos , I use them all the time. Just make sure they are YOUR photos.
You'll know when you get there!