Zcash halves its block subsidy roughly every four years, like Bitcoin. The first halving landed in November 2020, the second in November 2024, and both are marked on the rainbow chart.
In the year following the November 2020 halving, ZEC's daily closes ranged from $53.19 to $318.92. In the year following November 2024, they ranged from $29.23 to $698.43. Two events is far too small a sample to call a pattern, which is precisely why the rainbow's long-run regression is a steadier reference than halving folklore.