To me it depends on the "basic" primary tartan colors"

my "basics" are
1. Black Watch ( including my BW, Gordon, Seaforth (Mackenzie) Black Douglas etc.
Hose = Black, Navy, Dark Green.
2. Greys (such as my Auld Lang Syne - Grey, Night Stalker, etc)
Hose = Black, Charcoal Grey, Light Grey
3. Earth tones ( Tans & browns) ( such as my weathered Mackenzie)
Hose = Brown, Tan, Khaki

If I had to take only 6 hose then they would be
1. BLACK ( will go with # 1 & 2 kilts.)
2. Khaki (or brown) for #3
3. Dark Green ( for #1 & 3)

! would have a pair of each in a GOOD inexpensive hose like these from http://stores.ebay.com/WB-SOCKS_KILT...QQftidZ2QQtZkm & the khaki from WPG

I would also have a "dress pair )Black, Dark green, & Brown from http://giftshop.scottishtartans.org/hose_lewis.htm

Puffer