King Edward VII's Hospital Sister Agnes, Nurses Service badge

A scarce long service badge for the King Edward VII hospital in London. These were , I believe, awarded for length of service for number of years signified by different colours.Unfortunately I do not know which colours denoted what years, but if anyone knows I would love to hear from them?
This badge in a light blue enamel, to the centre is the crowned monogram of ER VII,King Edward VII,
Condition is good with pin,clasp and safety roller catch all good.

Code: 54747