Left: thread 糸, right: color 色 (top: bent person ⺈, below: 巴 var. of slumped Person 㔾 [In knitting often a colored thread is used do indicate the last row/border.]
Mnemonic
The thread is in color to discontinue or end (the fabric).
The app has many other functions, such as character selection according to difficulty, practice programs, handwriting recognition and success statistics!