At the top a growing plant (sometimes also 耒 or 丰, as with "life" 生) and below the moon 月. Accordingly, growing plants appear in the moonlight: blue/green.
The radical tsuki stands for moon or month when used at the right side of a character. However the radical niku肉 that stands for body or body-part is in many cases simplified to 月 and thus looks equal as "moon".
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!