Proposal for UTC offset coloring in maps based on 6 RGB colors

[Tobias Conradi]

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_zones.html
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).png.png
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_2010).svg
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