Lavender Meaning
Lavender flowers are known to represent purity, silence, devotion serenity, grace and calmness. In addition to the flower's significance, its purple color also comes with great symbolism. Purple is the color of royalty and speaks of elegance, refinement and luxury.Jan 5, 2017
https://www.1800flowers.com/blog/flower-facts/all-about-lavender/
Rat Corney is stating with the Lavender that he will remain silent, also asking others to remain silent. In the same time, with the color = purple, he is also stating he is loyal to her majesty HRC.