Even if you enchant the "Knowledge Book", the color of the item name does not change.

The Bug:
The knowledge book doesn't change the text color to aqua but keeps it as purple.

Reproduce

• Go into creative
• Execute the command 

  /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 should be aqua.