The properties of a substance which determine its color are chemical properties (the color is determined by the optical properties which are largely determined by the bonding interactions). Therefore a change in color is indicative of a change in bonding, which is a chemical change.
It depends on what kind of chemical reaction. lower energy chemical reactions are less likely to have color changes. in other words, there is really no way to answer. Just one note: color change means chemical reaction, but chemical reaction doesn't always mean color change