Keep in consideration different situational and permanent degrees of impairments while developing and prepare for the unforeseen
Situational impairments or changing conditions shall be considered when choosing colour themes and backgrounds of user interfaces. Solutions could be identified for other contextual conditions affecting perception, for all kinds of users and on different sensory channels (e.g. road navigation maps offering light-sensitive backgrounds, which change dynamically when sensors detect low-light conditions such as car galleries).
Assume users will rarely use the application in the ideal situation, on the contrary imagine all the potential deviations of use since they will show-up sooner or later. As an example, a non-exhaustive list of potential variations in the context of use emerged from the UIL exercise in the Antwerp pilot, related with street crossing (INDIMO UIL manual, Table 17).