What are the colour of your eyes?

I often find myself reading other blogs, in the name of "research", and finding myself jumping from one link to another, following one idea to another, storing lots of fascinating facts within my grey matter (in theory).

One of my favourites is Robert Kosara's Eager Eyes blog.  Recently, he was discussing writing as a metaphor for visualisation which led me, via a couple of hops, to an IBM research piece called "How NOT to Lie with Visualization", written by Bernice E. Rogowitz and Lloyd A. Treinish of the IBM Thomas J. Watson Research Center, Yorktown Heights, NY.

The article is a discussion of colour maps used in visualisation.  It is worth reading.

My own rule of thumb for a colour map is to use just the one hue - e.g. Blue, because it is relatively neutral - and change the lightness of the colour from one end of the scale to the other (e.g. using ColorMix functions in QlikView).  If I need diverging scales, then use two different hues that go from light in the centre to dark at the extremities.  For this, I always imagine an old ordinance survey map that shows sea and land - as the sea gets deeper, the blue gets darker; as the land gets higher, the brown gets darker.

Of course, there is always the question of ability to discern the difference in colours in between those extremities and whether a colour map is suitable at all - some humans are much better than others.  So what can we do for those of us whose eyes are not so good?

In many cases, I will implement a simple rule - anything that needs investigation based on the business rule gets coloured, everything else stays neutral.