You could use the alpha argument to set transparency to each color. The
overlaying colors should have a mixture of both. For example, see the
bottom two images (http://had.co.nz/ggplot2/geom_histogram.html) of how
alpha mixing works. Lattice graphics also have an alpha argument.


Cheers,
Roman


On Wed, Apr 25, 2012 at 12:13 PM, Juta Kawalerowicz <
juta.kawalerowicz@stx.ox.ac.uk> wrote:

> Hi,
>
>
>
> Does anyone know how to create mapping of attribute A and attribute B so
> that the overlapping areas are not colour A or B but the mixture of the two
> (the semi-transparent effect). In case that does not sound clear, I am
> looking for this kind of effect
>
>
>
> http://tinyurl.com/cko7c4b created by Divid McCandless (probably not
> using R?)
>
>
>
> If anyone knows a function/package which could allows to do something like
> this, I would be very gretful for suggestions.
>
>
>
> Cheers,
>
> Juta
>
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>
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-- 
In God we trust, all others bring data.

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