Beings of Tash Kalar
Imagine small totems or other ritual items placed next to the summon space.
The Ritual Keeper invokes natural magic of the summon space – grow if it is green, aggression if it is red. On other spaces, this magic does not work.
Ritual Keeper is one of the weakest beings in the entire game. If you manage to summon it on a colored space without much effort, the effect is nice, but if not, do not waste a turn preparing the pattern around a colored space and just summon him elsewhere to draw a stronger card.
The Ritual Keeper was created together with Ritual Master, as a small version of that card. Two orthogonally adjacent spaces instead of three diagonally adjacent, common piece instead of heroic, and the original effect allowed you to gain one action when summoned on green or destroy one common piece when on red space. It changed later, when I realized that Highland really lacks movement and upgrading effects.
Just before releasing, we were considering to strengthen this card a bit, as it is really difficult to use it well, but at that time, Highland was strong enough and we didn't want to damage the balance, so we decided to not change it at the last moment.