Beige, sand, khaki, earth, olive green, tan, fawn, erm, beige again, desert, caramel, tarmac, asphalt. Take your pick.
Red? Hmmm... I reckon your best bet is probably one of the European brands. I know Jack Wolfskin used to do a triple zip-off pant and they have normal zip-offs in 'rust' which seems to be a sort of dull red - called Pineland.
The Triple Zip are the triple zip and the JW web site is at: www.jackwolfskin.de
Sadly the Triple Zip only seems to come in shades of beige.