As the king in Sovereign Chess, there is a stark difference between the color you "own"--the color of your king--and the colors you "control", through occupying their matching squares. The pieces of your color are loyal to you always, while the control of other colors shifts throughout the game.
However, as the game progresses, your loyal troops may dwindle. Key pieces are captured, and you are more reliant on colors you control, rather than own.
Figure 27 has Black in trouble. Down to two knights, a bishop, and a few pawns, he is pinned in by Violet, controlled by White.
Black's only hope is in controlling the Red pieces, but White has just pushed the Violet pawn to d13, threatening Black's bishop. Moving off the Red square will cause Black to lose both Red and Slate, with little hope of regaining either.
Black's solution is to defect to Red, which has two major consequences. First, as Red, the player does not need to occupy the Red squares in order to move those pieces. He has, in effect, replaced his dwindling troops with a Red queen, rook, bishop, and three pawns.
Second, he has rendered the Black pieces invulnerable to capture, by Rule #12, temporarily creating a wall behind which the (new) Red king can take refuge from the impending attack.
Black's defection to Red constitutes a move, even though the king has not changed squares.
But what about the Black pieces left behind? Either player can control those troops by occupying one of the Black squares in the center of the board. Yes--it is possible for the player playing Red to be checkmated by the very pieces he "owned" at the beginning of the game!
The only condition on defection is that the player must control the color to which he is defecting. However, if the king is occupying the controlling square of color, then this would violate Rule #5--so the king must make a move.
In Figure 29, White is in check, and unable to respond without moving off Green. His Green queen is controlling Navy, and he feels his Green and Navy armies are stronger than what he has left in White.
His answer, in Figure 30, is to defect to Green, thus gaining sovereignty over the Green queen on Navy. Now, he must move off the Green square, and so retreats to Ash, immediately controlling that army. [Note that if all moves off the Green square would keep the king in check, then the defection would be illegal...]