It is my understanding that the entire Highland Brigade was kilted at the Battle of Alma ....
It is not clear which paintings you have seen or, for that matter, why you doubt their accuracy. - unless it is because you are familiar with other images showing the "1855 Pattern" Highland Doublet (a sort of "double-breasted coatee with Inverness flaps) which was not introduced until after
the Battle of Alma ......
I believe that the two best known paintings depicting the 42nd Regiment in this battle are "Alma: Forward the 42nd" (Robert Gibb) and "The Battle of Alma" (Felix Philippoteaux). So far as I am aware, they depict the uniforms quite accurately ..... as seen in this detail from Gibbs' painting -
The next rather fuzzy image is a detail cropped from a small (and poor) reproduction of a WWI-era print depicting the uniforms of the Black Watch from 1742 through 1914. It depicts the uniform as of 1852, which was worn until the 1855 Pattern doublet was issued -
Fortunately it is not necessary to rely entirely on artist's impressions. This very early photograph (reproduced in "The Black Watch Photographic Archive" published by the Regimental Trustees) shows officers and men of the 42nd Regiment in 1852, while stationed at the Citadel in Halifax -
Detail - regarding this man, the caption notes "The figure leaning on his musket to the left is Charles Christie who was drowned in the Ganges during the Indian Mutiny."
The distinction of wearing shoulder wings (normally reserved for Light Companies) had been granted to the whole of the 92nd Highlanders in 1822, and the same privilege was extended to all Highland Regiments in 1831.