As we know, there are three colours for the admirals. Namely blue, white and red. The three ranks, Admiral, Vice Admiral and Rear Admiral, always share one colour. But now there was one more, and that was the Yellow Admiral, and that was not a rank to be proud of. It was a position every captain dreaded.
Namely, the Yellow Admiral was a post-captain who would be promoted to Rear Admiral upon retirement without ever having served in that rank.
The pressure to create "yellow admirals" arose after 1815, when the list of post captains was so long that the prospect of promotion was low. Under the promotion system in place at the time, any officer who had reached the rank of post captain was automatically promoted when his seniority brought him to the top of the list and a position on the flag list became available. To keep these lists moving, post captains whose seniority brought them to the top of the list were promoted to the rank of flag officer the following day and placed on the retired officers' list so that they did not automatically fill up the list of rear admirals.