Ink’s and Admirals

You will all at sometime in your careers noticed different coloured ink being used by Commodores and Admirals when responding to correspondence or signing their names.  My recollection is that Commodore’s wrote in Green ink and Admiral’s wrote in Red.  Can anyone else add to this or am I colour blind?

From the comments received I thing the answer is as follows:

In the days of the Naval Board the First Naval Member (CNS) signed in Green, the Second Naval Member in Red and the Third Naval Member in Purple. Later CNS signed in Green and DCNS in Red and Comauck for local issues Green.  This was not prescribed rather a custom and there will be many exceptions.  Thanks Karl M for the clarification.