Neutral light is preferable for headlamps since it helps discerning colors and shapes: cool light tends to significantly wash shadows and dark surfaces out—this ends up in a loss of visual contrast and general shape recognition. It's not a problem indoors where potential obstacles are easy to recognize and avoid, but definitely not something you'd want to give up when climbing, caving, or biking. If you only have one main light source on your trip, you should definitely consider something neutral.