I'm the type of nail polish addict who loves to paint the season. Pastels in Spring, Neons / brights in Summer, Muted colors in Fall and the Classic Red, Gold and Green during Winter. Here is my round up on some stable colors for me this season.
Just a heads up, the colors I'm about to mention doesn't necessarily mean that there this years trend or 'in' color. This is just my opinion on what I think best suites fall.
Browns & Gray: I can't tell you how much I love Gray during this time of year. The weather is finally cooling down and the only thing I want on my nails is a color to match the weather. Gray's are a perfect shade to wear during Fall and a definite replacement if you don't own a nude shade. One of my absolute favorites in NYX Girls 'The Taupe' (Swatch).
Purples: Sometimes you need a little pop of color, even if it's just an accent nail. That's where the purple comes in. I personally think that Gray and Purple mix really well together and would have no problem being neighbors if you decided to do an accent nail for either colors.