MacRobert,

Calling a tartan a "dress" tartan does not imply that it is meant for formal wear. It generally refers to a tartan which has much more white in the design (though there are exceptions). Indeed, one could wear the Hunting Robertson to a formal event just as readily as the red Robertson tartan.

The STM has this handy little sheet available for download and photocopy which deals with these confusing tartan terms.
http://scottishtartans.org/downloads...eet_colors.pdf