Hey you are using this plugin as your Visual Editor for posts Advanced Editor Tools (previously TinyMCE Advanced) – WordPress plugin | WordPress.org
There is no such option to register colors to use. However if you switch to Gutenberg in that we have option to register default primary colors.
Also i would recommend you to use Gutenberg that is more powerful and new Visual editor for posts. If you want i can disable this Classic editor with new Gutenberg editor so you can try.
I added your given color in custom colors also updated it but his is not saving , i searched their plugin notes and support section still no help.
This is where i tried to save your custom color.

But if you wish you switch to Gutenberg there we have option to modify colors like this
