Stuart, the SH were only originally formed to compose one regiment, laterly a second was formed. So the first regiment would not have chosen yellow as a flash (I call them flashes as thats what we wore back in my para days!), this is backed up in the book 'southern cross scots' and where it identifies the patch as murray of athol tartan (oblong but also squares). Although I do admit the information is not detailed. The yellow and red may have come in during the later part of the Boer war but I doubt if anyone would have wanted to change the murray tartan in such a high espirt de corp and close knitted unit. Also the pictures I've seen either have tartan or dark patches (although I know some yellows go dark on period pictures)! I conjecture that the red/yellow came in after the unit was reformed in later part of 1902.
Also agree on different badges - the early contingent wore field cut badges oval with 'X' and 1900, the newer Scottish contingents wore a circular stamped cross see my avitar! No doubt when they came together then they probably unified things! But one thing I'm sure off is that some say that the 'ScH' badge was worn on the hat, I really don't believe this, it was a shoulder title!
Yes its grey and murky out there, than goodnes they had some form of cameras otherwise it would be very murky!!
p.s. notice the lack of a feather plum in this picture! Again I think this depends on where the pictures were taken and issue of kit etc!