Been buying and selling for over 40 years. 90% of the time I get what I ask.
Most of the time when a seller gives you a better price because of some fluff like "the color", it's because they already had inflated their price and the offer was better than what they intended to let it go for in the first place. That's how it goes. The next guy to look at it wouldn't give two sh**s about the color, but the seller just got a better price than he actually had in mind. That's the game some play.
With me, I price things fairly, you know how it's equipped and what color it is before you come to look at it. You know the price, so it must be acceptable. Try to excessively dicker with me over that kind of stuff, or because it "isn't quite what you were looking for", and all it will get you is "escorted off my property".