Roses are red and violets are blue... we would only know this because light is reflected in our retina which then sends a signal to our brain. Color perception is based on the reflected light but any change in the light source can hugely affect the colors we perceive. As an artist you must have experienced this problem - you start working in the morning and by the time you finished an element the light changes and colors no longer look like anything you may have anticipated. As an artist having good neutral lighting is key to improving your painting and color mixing.