Christios --
I cannot find any way to specify the default font, size, and color for the text in task notes. I tried inserting the Notes column in the Gantt Chart view, selecting the Notes column header, and then applying a different font and font size. Although it
formatted every entry in the Notes column with the new font and font size, and even formatted new notes with the correct font and size, this did not change the font that is displayed on the Notes page of the Task Information dialog.
In Microsoft Project 2013, I noticed that the default font is Segoe 10 point, but I could not find a way to change it for every note. Also keep in mind that if you do a straight copy and paste from a document, Microsoft Project tries to keep the original
font, font size, font formatting, and font color when you paste the text. The alternative is to do a Paste Special and paste only the text. This way you will see everything formatted with the same font.
Hope this helps.