Possible Clues:

• Kind enough to be in command before half a century
• They're kind to a green mixture
• Perhaps they're kind to a green
• A further fifty would make them kind in command
• How kind of them to give fifty it would be to make him the commander
• They're kind enough to put him in command if he gets to fifty
• They could be a kind of a green
• Cut non-specialised classes
• Species that high-ranking officer left out
• Taxonomic categories (biology)