If you can effortlessly hear chord tones, then playing improvised solos over a set of unfamiliar chord changes (particularly during a jam session), drastically simplifies.
Recently, I came across two websites that provide chord progressions and even single chords of various qualities, that can be used to practice focusing on hearing chord tones.
Two Websites That Can Be Used To Practice Hearing Chord Changes
http://www.playingthechanges.com/ This website allows you to download 72 single chords of different chord qualities.
http://www.zogmusic.com/EarTraining.htm This website provides methodical chord changes.
Once you are familiar with being able to hear chord tones, then hearing changes becomes the next challenge to accomplish. The chord tones will not sustain very long until the next chord is sounded. So you’ll have to hear and process quickly.