Once again, here is a great article from Inside Out Style. Imogen responds to a question to clarify what colours are considered neutrals.
Like she mentions, neutrals are great staples in your wardrobe as they provide a basis for other colours to shine! You can combine them with many other garments and no-one will notice that you are wearing the same neutral coloured jacket, trousers, skirt...
Here are some examples from my wardrobe: Navy & White check (works as a neutral for my plainer tops, also the navy passes as a black as it is quite dark), Navy, Med Dark Denim, Charcoal, Silver / Light Grey, Med Light Grey (front), Taupe check.
I like having a mixture of colours and depth of value (dark to light) within my neutrals, but they have to work with the majority of my tops. I find I wear medium to med dark pants mostly as the majority of my tops are also medium to med dark in depth. But I enjoy the med light to lights as an alternative when wanting a lower contrast with my lower depth valued tops. I also enjoy using different weaves / patterns in my neutrals to add some interest.