Enchanting rare items doesn't change the text color

The Bug

Enchanting rare items such as a command block or knowledge book doesn't change the text color to aqua but keeps it as purple

Reproduce

• Go into creative
• Do /give @s knowledge_book
• Get an anvil and enchanted book
• Enchant the knowledge book

Observed Result

The text color of the enchanted knowledge book is still purple

Expected Result

The text color would become aqua