How To Hear Differences in Chord Types

Each type of chord gives off a mood of its own. By associating the mood, or emotion, with a specific chord type, you can soon learn to distinguish between the basic kinds of triads:

Major

Minor

Diminished

Augmented

For example, minor chords sound more somber, more serious, than major chords. Why? Because of the way the intervals are "stacked" within the chord. A diminished chord sounds suspenseful, tense, nervous. An augmented chord has a distinctive sound, too. Learn how to hear, feel, and identify these chords, as well as extended chords (you'll learn how to listen for the "color tone" in any 4-note chord).

Here are the color tones we'll listen for:

6ths
7ths
9ths

Once you can identify the 4 types of triads, and then recognize the color tones, it is a short step to recognizing chords such as minor 7ths, minor 6ths, diminished 7ths, major 9ths, and so on.

http://www.playpianocatalog.com/ear-training-chords--how-to-hear-differences-in-chord-types.html