This proposal is restricted to UTC offset zones, i.e. it does not propose anything for the tz zones. In the following text main zone will refer to any zone with an offset from UTC that is a multiple of 1 hour. ==Current situation== http://www.worldtimezone.com/ uses 3 colors, RGB, for main zones, as of today the map on the home page shows Kyrgysztan as +5 in the same color as neighboring China +8. repetition after 3 hours https://www.cia.gov/library/publications/the-world-factbook/maps/refmap_time... uses 4 colors, 2 kinds of green, 1 brown, 1 yellow for the main zones. repetition after 4 hours http://www.worldtimeexplorer.com/WorldMapBig.gif uses ca. 9 colors, main zones and zone with other offsets share colors. repetition: none, e.g. orange in America is preceded by grey, while in Asia it is preceded by cyan Wikimedia offers maps with several different schemes: http://commons.wikimedia.org/wiki/File:Worldwide_Time_Zones_(including_DST).... ca. 9 colors, includes coding for DST usage Even where the following files share offsets from UTC, the colors are not necessarily shared: http://commons.wikimedia.org/wiki/File:Map_of_Russia_-_Time_Zones_(2009).svg http://commons.wikimedia.org/wiki/File:Sakha_time_zones.png http://commons.wikimedia.org/wiki/File:Map_of_Russia_-_Time_Zones_(April_201... http://commons.wikimedia.org/wiki/File:Time_zones_of_Europe.svg http://commons.wikimedia.org/wiki/File:Africa-timezones.png ==Proposal== Use 6 colors that are easily distinguished for the main zones and order them so that mixing two colors from two zones that are 2 hours apart result in the color of the zone in between. The same mixing process shall be applied for zones with an offset of 30min from a main zone. The RGB space, if each color can only be on or off, gives 2*2*2=8 possibilities which include white and black. That means there are 6 colors (Level 1 colors) that can be used. One possibility, denoting colors in hexadecimal shorthand form (f = ff, 0 = 00): UTC = f0f magenta +1 = 00f blue +2 = 0ff cyan +3 = 0f0 green +4 = ff0 yellow +5 = f00 red The repetition starts with +6 = UTC = f0f. As middle position between x00 (0) and xff (255) use x80 (128) as listed at http://www.w3.org/TR/css3-color/#html4 The zones with a 15min offset from a main zone get to use 40 (64) or c0 (192) e.g. +5:45 = ff00c0 (used in Nepal) Even if the colors apart from the Level 1 colors are not desired because they are too difficult to distinguish, one can use the main colors. One can memorize: +1 = CET most parts of the EU = base color of the EU flag +3 = Arab Standard Time, Mecca lies in the +3 zone = green = base color of the flag of Saudi Arabia The one can derive that the color for the zone in between, namely +2, is cyan. Since colors repeat after 6 main zones, +8 will also be cyan. A matrix of colors and offsets can be found at: http://www.tango.info/wiki/UTC_offset_representation_by_6_base_colors If anyone can make a map of the UTC offsets using 6 base colors, not necessarily those that are used in the proposal, I would be happy to see it. Any suggestions for improving the system are welcome. -- Tobias Conradi Rheinsberger Str. 18 10115 Berlin Germany http://tobiasconradi.com