Thanks for the link.
The question is, "What voltage levels are required on the digital inputs for a logical Low and High?".
See the section: Electrical Characteristics
High-level Input: 0.7 x VDD
Low-level Input: 0.3 x VDD
For both, the required voltages are relative to VDD. Therefore, if VDD is 12 V, then >= 8.4 V is required for a logical high and <= 3.6 V is required for a logical low.
@VDD == 12 V
High-level Input: >= 8.4 V
Low-level Input: <= 3.6 V
This is the spec you must meet for the LEDs.
A next step would be to determine the High-level and Low-Level Output voltages of the level shifters on the OctoWS2811 (74HCT245).
It would then be known exactly what voltages must be translated from and to.
[Edit]
SN74HCT245, IOH, IOL = –20 μA
High-level Output: >= 4.4 V
Low-Level Output: <= 0.1 V