A method for determining if an object in a colour three-dimensional environment rendered in real time on a display by a computer is visible for user with a defined point of observation in the three-dimensional environment. The object is defined by at least one area with a predefined colour (CD) where said area is rendered with a colour (CR) that is different from the predefined colour due to the rendering conditions at a defined time point. There is a pre-defined pseudocolour (CP), where a colour is defined as colour values for each of the red (R), green (G) and blue (B) channels.