Unlike most other Outlook folders, the Notes folder offers only a few settings. You can change the color Outlook uses for new notes, the note font, and the initial window size for new notes. You can change the font used by all notes but not the font used by individual notes. In other words, all notes have the same font and font size. However, you can set note color individually by assigning a color category to the note.
Right-click a note.
Choose Categorize from the menu.
Select a color category for the ...