I should point out that in the photos I posted no belts, buckles, or other "finery" makes any appearance. Most of the men are wearing quite plain brown or grey jackets, jackets so ordinary that we don't see them worn with kilts often today.

Actually there's one bit of finery, the relic brooch being held and displayed (not being worn) by one man.

Three things stand out in these images which differentiate their plain dress from 20th century "day" dress

1) wearing plaids wrapped around the body rather than sitting on one shoulder per the 20th century style (the so called "laird's plaid")

2) wearing long hair sporrans with plain dress. I point out that these long hair sporrans were the common style of the day and were worn with all modes of dress. We today expect the plain leather pocket "day" sporrans with ordinary dress but these aren't seen at that time, and it's anachronistic for us to expect mid-19th century men to follow 20th century styles and wear 20th century things.

3) wearing tartan or diced hose with plain dress. Yes in the early 20th century Highland dress became compartmentalised with tartan or diced hose reserved for evening, but again we need to guard against projecting 20th century styles on the mid 19th century. Note, by the way, that the tartan hose are usually of a different tartan than the kilt.