YA fantasy where main character is an assistant or apprentice to a woman who is working on creating a new color

[Amna]

they end up creating an entirely new color and it’s so beautiful that they are moved to tears. i don’t think this was the main focus of the book but it is they only part i remember. i think the new color was supposed to be made to be worn by royalty or something like that. also there’s a mechanical spider as a sidekick i think?

[Bryn]

The Cabinet of Wonders sounds very likely -- reviews mention both the mechanical spider and the invention of a new primary colour.

[Kris]

Here's the Google Books preview of The Cabinet of Wonders by Marie Rutkoski - Bryn's suggestion - https://books.google.com/books?id=NdT... There are different cover images.