The TKD is the distance between the Tenkan-Sen and the Kijun-Sen, expressed in percentage of current price. The further apart the tenken-sen and kijun-sen are, the more they want to snap back together. This makes for a decent oscillator. When the Tenkan-Sen is above the Kijun-Sen, the TKD is green. When it is below, the TKD is red. At the crossing points, it turns blue.
For those more familiar with Ichimoku Cloud techniques, one might also think of this indicator as a C-Clamp indicator. Bar coloring is supported and enabled by default. There's also an option to flip/invert the green/red colors in case you want to use it to judge pending cycles rather than current ones.