[AUCTeX] Controlling colours of preview images

[Marco Gualtieri]

I would like to change the colours used for previews generated by preview-latex.

The behaviour without customization seems to be black text on white
background if I use a light theme,
and black text on dark background if I use a dark theme.

I have tried to customize Preview Reference Face, and I seem to be
able to change the background colour of the .png files using this, but
not the text colour.

Also, I looked into the source of preview-latex and found a variable
preview-colors; I tried to set this to an array of colours (there
seems to be an inconsistency in preview-latex.el about whether it
should have 4 or 3 colour entries) but this had no effect at all.

Summary: how do I control the preview image colours?

Thanks
Marco