Daytime flight rules are based on the pilot using visual search technologies to observe other aircraft and thus avoid collisions. One way to make it easier for pilots to detect other aircraft is to increase the visual signature of aircraft in general. With regards to the upcoming acquisition of new trainer aircraft for basic flight training, the Swedish Armed Forces commissioned the Swedish Defence Research Agency (FOI) to investigate, and suggest an appropriate colour scheme for maximum visibility. The main question was: what colour should be used to provide as high visibility as possible in order to facilitate visual contact between aircraft taking part in the same exercise and under varying lighting and weather conditions. A literature review revealed several factors that influence the choice of colour, but visibility has not necessarily been the main factor guiding choice of aircraft colour historically or internationally. In order to arrive at suitable colours for maximum visibility in a Swedish context, an experiment was conducted. The experiment included seven colour samples (red, orange, yellow, green, blue, violet and white) and seven backgrounds corresponding to ground and sky. Based on the experiment, in combination with what has been said in the literature, the use of two colours, orange red top and dark blue underside, is recommended as it is expected to work against as many different backgrounds as possible.