Matching jacket and waistcoat?

[MacMillan of Rathdown]

Piperdbh seems to have summarised it well. Strange that the most formal (white tie) and least formal (tweeds) are where waistcoats that don't match the doublet or jacket are most often worn.

Actually, unless one is wearing a Sheriffmuir doublet, a white waistcoat is de rigueur for wear with a regulation doublet or Prince Charlie coatee. When dressing for black tie there is more latitude, and both tartan and a variety of solid colours, as well as black, may be worn.