I know there's no solid "rules" in music and it all depends on the feel of the song, etc, but if the chord doesn't list it, can you play more than the triad or pentatonic scale?
Example if I come across a C major chord, should I just play the triad and pentatonic, or could I slip in a 7th there? What if I wanted to add some colour with a #11th, would I be asked to stay in the realm of the chord or would it be encouraged?
Hopefully that makes it clear...