The chromatic mediant is another type of out-of-key chord. The word chromatic means any note outside the key, and mediant refers to chords with roots that are a third away from the root (first note) of the key. It can be a major or minor third above or below the root of the key. In the key of C, the 3rd note is E, which is a major third (4 half steps) above C. Therefore, the three chord (iii) is the mediant. Note A is a minor third (3 half steps) below C, so the six chord (vi) is called submediant.

There are three chromatic versions of the mediant and three chromatic versions of the submediant. In other words, there are three chromatic mediants based on the three chord (iii) and three chromatic mediants based on the six chord (vi). These chords have roots that are a third away from the root of the key (mediant), but they have at least one chord note that is not in the key (chromatic), hence the name "chromatic mediants." In the video I demonstrate how you can easily build them.

The song in this video was originally a slow tempo song, so I slowed down the tempo for the revised version and added chromatic mediants to the progression. Chromatic mediants are known to resolve to the one chord for stability. However, it is possible to delay the resolution by adding more unstable chords before the one chord. This is a great way to make the progression less predictable and more interesting.

Edit: Sorry about the sunlight in the beginning of the video, it eventually leaves.

https://youtu.be/SQsWS2v39no