You might be surprised to learn how many male skippers suffer from some degree of colour blindness. The sea’s rules and regulations do little for this silent minority, but one area where a clue can be found is in the numbering of buoys and beacons. Reading from seaward, channel markers are always numbered in rising order, with green, starboard-hand buoys or beacons bearing odd numbers.
Reds on the port-hand are even. If you come across a single marker of indeterminate shape without a topmark and can’t identify the colour, check its number for the answer. Even full-vision observers can have a struggle with colours in poor visibility and awkward lighting. The numbers are a useful help.