The dress code will be sent to you with your tickets. As a general rule on Fred. Olsen ships there are two formal evenings each week (men wear dinner jacket or dark suit), and the remainder a mix of casual (first & last nights and sometomes overnight in port) and smart informal. There are also "theme" nights eg tropical, British (red, white and blue), Western. Daytime is, of course casual although swimwear is not allowed in the main restaurants.
Hope this is of help.