Thanks for the feedback Yoni. Good questions!
Medium’s interface is consistent, not allowing to change the UI. In some way, this is great, since all of the articles turn out to look consistent, which is easier for the reader. In addition, the main focus on Medium is on the text, so in that situation, leaving the page white would be OK, since they don’t want us to focus on other elements. Interestingly, when you go to manage the responses, where I’m writing my response now, the background is light grey and the responses are managed on white cards that stand out, and allow to focus the attention on the response itself.

As for the color selections, I’m not sure which element was different than the color codes I wrote, but the reason I gave a specific code to choose was to reduce the need to select for those lacking the skills to do so. Actually, it doesn’t really matter if this is the exact code I referred to or any other tone around it. I can’t say I’m always choosing the exact same red, in cases where the UI doesn’t let me personalized the color picking control.