Possible Clues:

• A deep-blue colour
• Young animal entertaining the graduate element
• Steel-gray element
• Metal in gun used to hold up sailor
• Metal that gave its name to a shade of blue
• A deep-blue colour (6)
• A junior officer on horse is in one's element
• The horse starts till all is blue & Co. symbolically
• An officer on a horse shows his metal
• Sounds a little hoarse around the graduate till all is blue