It's not really a histotechnique (at least not a microscopic one) per se,
but there is a method in which the arteries and veins are injected with
contrasting colors of plastic, and then the entire organ (or piece of it)
is dehydrated and cleared in methyl salicylate so that it becomes
transparent and the vasculature shows through. It then becomes a lovely
conversation piece.
I can't give you a reference, but I hope that someone will chime in with
the details. 

Jeffrey S. Crews, HTL (ACSP)

On Fri, 20 Oct 2000 15:31:14 -0400 Darren Robinson <DRobinson@ciit.org>
writes:
>Wise-ones,
>
>I once met a bloke at a conference who told me that he had been
>investigating the distribution of the arteries and veins in one of 
>the
>major organs (I forget which one).  He described the staining 
>proceedures
>he was using to me and said that the stain coloured the arteries blue 
>and
>the veins red.  This impressed me to no end, but I walked away from 
>him
>without asking what the name of the stain or combination of stains
>was/were.  Now he may have been pulling my leg, this sort of thing 
>does go
>on at conferences, but I would like to know if any of you out there 
>have
>heard about or used a staining technique like it.  Also, if it turns 
>out
>that he was pulling my leg, does anyone know of a good stain that 
>will
>allow me to differentiate between the arteries and veins in wax 
>sections.
>
>Darren.
>
>P.S. If you are the man who pulled my leg, I demand an apology.
>
>
>