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Color palettes to convey information to color-impaired viewers and on different output devices

Question:

Which of Ferret's color palettes best convey information to color-impaired viewers?

What palettes will show up well if I photocopy the output, or display it using LCD projectors, Laptop and CRT screens, and color printers?

Explanation:

The article "The End of the Rainbow? Color Schemes for Improved Data Graphics", by A. Light and P. J. Bartlein, (2004) EOS 85(40), p. 385, 391 discusses shortcomings of some of the common color schemes used in scientific publication. It explores types of color palettes which better distinguish the desired features of the data. This article is available on-line at http://geography.uoregon.edu/datagraphics/EOS/index.htm

Articles and notes on this topic from EOS are available at http://geography.uoregon.edu/datagraphics/EOS/Light&Bartlein.pdf Look at the last few pages for a response to the original article "Forum: Comment on Color Schemes for Improved Data Graphics" and the reply to this comment. These make a helpful discussionof the issues involved and useful color palettes for different sorts of data.

Solution:

We have implemented as Ferret palette files some of the color schemes discussed in the EOS article and the two web sites it references. Their palette names, some of their properties, and a simple example of each are in the tables below.

Recall that in Ferret you can change to a new palette using the /PALETTE= qualifier on a SHADE or FILL command:

   yes? SHADE/I=1:10/J=1:10/PAL=green_magenta i-j
   yes? FILL/I=1:100/J=1:100/PAL=blue_darkred cos(i/8) + sin(j/6)

   yes? PALETTE blue_green_yellow
   yes? USE etopo20
   yes? SHADE rose
   yes? FILL/x=12w:35e/y=25:60 rose   ! this plot also done with blue_green_yellow

   yes? USE levitus_climatology
   yes? PALETTE red_purple   ! change to red_purple palette for next plots...
   yes? FILL/K=1 salt

Most of the palettes here are listed in pairs, e.g. blue_green_yellow and yellow_green_blue. These pairs contain the same colors, in reverse order. The purple_red and red_purple palettes contain different sets of colors; purple_red having dark red to light purple and red_purple having dark purple to light red.

Name	Type	Color- blind	Photo- copy	Example
blue_green_yellow yellow_green_blue	sequential	Y	Y	example script
green_brown green_brown	diverging	Y	N	example script
purple_orange orange_purple	diverging	Y	N	example script
yellow_orange_brown yellow_orange_brown	sequential	Y	?	example script
orange_red red_orange	sequential	Y	Y	example script
purple_red	sequential	Y	?	example script
red_purple	sequential	Y	?	example script

At the University of Oregon site, a number of palettes are defined and discussed. Here is a list of several that we have implemented for Ferret, with comments from the University of Oregon Data Graphics Research group. For all of these palettes except the last, categorical_12_step, there are pairs of palettes which contain the same colors in reverse order.

blue_darkred darkred_blue	Useful for temperature-like data, with a subjective interpretation (blue=cold, red=hot)	example script
blue_brown brown_blue	Useful for data with a dry (brown) vs. wet (blue) association	example script
blue_darkorange darkorange_blue	Useful for data without a specific subjective color association	example script
blue_green green_blue	Useful for data with a winter (blue) vs. summer (green) association	example script
blue_orange orange_blue	Bright blue to Bright orange colors. Useful for data like sea-level pressure, with a subjective association (blue=low, wet, orange=high, dry)	example script
green_magenta magenta_green	Useful for generic diverging data. Colors can be differentiated by color-deficient viewers	example script
categorical_12_step	Attempt at a categorical color scale with colors that may be distinguishable to all viewers	example script