The picture looks to be c1860-90 and to be a mix of military/civilian dress although it may be wholly civilian in military style. That said, the white belt and cut of the jacket make me wonder if it was the uniform of one of the local Volunteer Units. Unfortunately no amount of image playing makes the buttons more distinct.

The tartan is a 42nd type but again, the quality of the image and fold of the cloth means that it could be one of the decorated variants such as Breadalbane. The sett appears quite bright but this may well be the effect of colours photographed in early B & W. Red often appears pale compared to blue, black and green; so the jacket could be red or some other colour such as grey and the tartan could equally be the 42nd Fraser setting.

What's the relevance of the Stewarts of Dingwall reference?