I've previously posted a bit of detail on the Rosettes (ribbons) worn by the Black Watch and now RRS so I've just cut and paste the detail here

The rosettes that are specific to The Black Watch, this one dates back to the 19th century. In those days Regimental Colonels had to purchase uniforms for their soldiers out of their own pockets and much money was spent trying to make their troops look as grand as possible.

In an attempt to save money at one point one Colonel decided that the overlap in the apron of a kilt was unnecessary and just a waste of material. Fine in principle but embarrassing in public having just purchased a new Regiments worth of kilts the Colonel was somewhat concerned that he was going to have to purchase a further regiments worth of kilts to solve the problem until a young officer in the unit suggested tying the front to the back with some green ribbon hence the rosettes were born. This is the reason the rosettes are somewhat less "grand" than those worn by the Argylls.

The Rosettes are only worn by Officers and SNCO's even though they are "very simple"