Engineers, Artillery, Highland Regiments or Light Infantry? Cavalry? Officers, NCOs, or other ranks?
Here’s what the Canadian Militia was wearing during the 1866 Fenian Raids; it’s very similar to the British Army uniform of the time: http://www.pinet.on.ca/peeldiglib/Page.asp?PageID=6702
Osprey publish excellent guides to uniforms and equipment, from Roman times to the Gulf War. The cover of this one shows typical British Army officer’s field uniforms of the Crimean War: http://www.ospreypublishing.com/title_detail.php/title=S1869~per=8
Here’s a reproduction uniform supplier in Wales, UK; there are some very nice colour images of repro headgear, equipment, uniform, etc.: http://www.thinred.co.uk/
Here are some friends of mine who dress up in the uniform of the Royal Engineers and Royal Artillery in British Columbia, 1858:
http://www.livinghistory.co.uk/1800-1900/portraits/xw_120.html
Here’s a contemporary watercolour of some Royal Engineers (in the UK), circa 1860: http://antiques.goantiques.com/cgi-bin/texis/scripts/mainsearch/auxdetail.html?num=2&did=3aa5126a25
There’s a pretty wide range, but in VERY general terms, infantry were in red tunics with blue trousers, artillery in blue jackets with blue trousers (with a wide red stripe), engineers in red jackets with blue trousers. Light Infantry and Rifles were in a very dark green, highland regiments wore a red jacket and a kilt, lowland regiments a red jacket and tartan trews (trousers).
Things were very different in hot climates (India, West Indies, etc), and white tropical uniforms were issued to some regiments. Officers often went rather “native” in the field; there is a photo of a British officer in British Columbia in the 1858 gold rush in a finged buckskin jacket that would have made Custer envious!