Change color of badge created with Metafield

[rougeon]

Hello, 

I was able to create a "new" label on my products using this guide: https://support.maestrooo.com/article/75-collection-displaying-custom-label 

https://ateliercomplice.com/collections/cake-toppers?page=2

However now I would like to change the color. How can I do so?

thank you for your help.