I’m not aware of an attribute that controls the color of the title of a note when in outline view. Am I missing something?
The colour of a note title in Outline view is the attribute
Color. This is used as the primary colour of a note icon in Map view. If you wish the map view to use a specific colour for the map icon’s title text, set that using attribute
And if you want to color the background of the note in the outline — often the best visual marker for outline view — use $OutlineBackgroundColor.