Playing chord tones while soloing is basically emphasising the notes that go with a particular chord while playing in a root scale. It’s kind of playing modes without thinking about modes. There are some differences and modes are important to know, but is actually a good practice to get into playing chord tones so your solos will sound more organized and cohesive.
PLAYING CHORD TONES
If you’re playing in C – the first chord is likely C Major, which is C, E and G.
If you go to the IV chord which is F Major – the notes are F, A, and C.
So as you’re soloing and the backing chord is playing, you can play all the notes in the C Ionian scale, but pay particular attention to the C, E, G notes – make them stand out. Then when the F Major chord happens – play all the same notes from the Ionian mode, but emphasis is on the F, A and C notes.
A good practice is to go over the individual notes of the chords as they’ll be coming up before playing so that you know where to play as the chord happen.