Mimosa tea I observe is a barky brown color. When adding a strong base like KOH, a gray precipitate instantly forms on the surface, and as it forms, the brown barky color disappears and the solution turns black. This does not happen with calcium hydroxide, no precipitate forms. Is this gray precipitate tannings being precipitated by the strong base? I've observed in the past that keeping adding the strong base, there hits a point where the color of the liquid abruptly turns from black to gray. Is this redissolved tannins being salted out by the ionic base?

Calcium hydroxide seems to precipitate something that turns the liquid gray. Adding potassium hydroxide dissolves the precipitate and the solution turns black again. My only guess to what this means is that the Ca(OH)2 forms an insoluble calcium tannate salt. Adding the stronger KOH converts it to the potassium tannate salt which is soluble in water.

The calcium tannate hypothesis seems likely to me too. The KOH might also hydrolyse the more complex tannates into gallates, and calcium gallate could well be more soluble than the tannate.