wasn't there also a "polo" red?

yes and no...
 

there was a Polo red available on early cars, but none of the RS/RSR cars were painted that color.

I almost bought a 1967 911S race car that was Polo red, sliped through my fingers though. I still ended up with a red car however ;)

Here are two red ones.
I know you asked for '73 models, but I had to include this VERY wide and very red '76 RSR.

Whenever I hear someone refer to a color as "Porsche-red", I think of Indish Rot (Indian Red). Bright red with a tint of orange.
I did a search on "red" at Paintscratch.com , but couldn't find Indian Red there. Is the name Indian Red actually used in the US?
Indish Rot matches (on my computer screen anyway) some of the many shades of Guards Red. The '75 to '80 Malaga Red is close too. :confused:

http://www.paintscratch.com/search.htmhttp://forums.pelicanparts.com/uploads/00363.jpg http://forums.pelicanparts.com/uploads/76RSR001.jpg