Found a supplier of red capless bulbs for my 1999 stepwgn which has non-coloured rear clusters.
<http://www.powerfuluk.com> has red 12v 21/5w capless (part number BRT203, red 12v 21w capless (part number BRT275) and amber 12v 21w capless (Part number BAT200) at £2.00 each inc VAT, - web-site shows same price today (January 2011).
<http://www.astraautomotive.co.uk> has red 12v 5w capless at 0.96p (but sold in 10s)