Everyone has their own choice but my favorite color is Lagoon. It looks classy and I love it.
Everyone has a personal choice and there is no such thing about the best color. Classic 350 looks nice in every color. There is a good range of black, white, chestnut, blue, maroon etc. colors are available in the market and you can choose any one of colors from them.
But if you are still confused and can't decide, then in my opinion if you are a die hard bike lover and you will love to polish your bike at regular intervals to keep it brand new and classic then go for maroon or blue, Classic looks very stunning and sporty in these colors. But If you can't spare that much time and regular cleaning and polishing isn't your cup of tea then go for silver and black.
These colors don't require that much attention of yours and very durable to heat and dust. Your bike won't look dull even after being driven for years. My personal favorite is also black!