I'm taking archery lessons at the moment too, and this thread caught my eye. A little casual surfing on whether kilts were appropriate for the range led me to this site:

http://archerynationals.com/08nation...gistration.htm

Excerpt:

3.1.18 Dress Regulations [similar to FITA 3.22]

(Jumping ahead to the rule in question)
3.1.18.3 Pants, shorts, skirts, divided skirts, etc. must be a solid unpatterned colour and may not be shorter than the fingertips when the arms and fingers are extended at the side. Blue jeans and fleece track pants are not allowed. (Bold mine)

The rule says nothing about kilts, but I guess this means that if you are competing in a FITA (International Archery Federation. The acronym is from the French) tournament, tartan is out.
Any experienced archery know why the emphasis on non-patterned clothing? Visual distraction perhaps? And why does it only apply to bottoms?