Stuart
They are standard feathers made to look like cock feathers, since real ones are impossible to find due to them being a protected species these days!
Dont know about the yellow folds, its not mentioned anywhere in the Boer war info I have, is it a post-boer war thing?
I'm only studing the SH during the boer war period at the moment but I do know they changed to Tam-o-Shanters at some point post Boer War but not sure when!
The flash is taken from one of the books I have, it appears to be Murray tartan, the only doubt I have is that there may or may not be a yellow or red 'line' to the right of the flash but it could just be the picture! I'm pretty sure the yellow/red etc flashes did not come in till post Boer War!
Mike