"Light infantry soldier of the 48th Regiment of Foot, 1759-1760 - "During the Seven Years' War, the British infantry regiments in North America converted one of their ten companies into a 'light company.' These men were trained to fight in the forests. Like the other units, the light infantry of the 48th Regiment of Foot modified their uniforms to match their new role."
I actually found the explanation above from a Pinterest post of the same image. (P.S. Pinterest is actually great when you wanna find images of 18th-century European uniforms.)
The 48th took on several hundred reinforcements in Alexandria Virginia in preparation for the campaign against French Canada in early 1759. These would very likely have been colonial volunteers or retasked militia, so that might explain the basic uniform, especially for light troops.
I can't find any documentation of the 48th being issued anything other than red uniforms: http://www.kronoskaf.com/syw/index.php?title=48th_Foot
The page OP's image is originally from is from the Canadian Military Heritage Centre. The page itself goes into some detail about light infantry uniforms of the late-war period, and it appears the 48th stayed fairly true to George Augustus Howe's reforms implemented during the Ticonderoga campaign of 1758. Coats were cut short and worn with the facings buttoned across, cocked hats converted into "jockey" caps with ear flaps, and swords exchanged for light infantry axes.
So all in all, the image you've posted isn't atypical of British light infantry of the French and Indian War. They're a derivation of battalion company uniforms, and are even farther removed from grenadier company uniforms.
For a quick, easy introduction to the uniforms worn in the time period you might want to check out:
