Measured on an ASRock Intel Arc B580 Steel Legend, which uses this same
packet: holding everything else fixed and stepping data[5] through 0xFF,
0x40 and 0x00 dims the zone progressively and turns it off at zero, while
data[4] does not change brightness. So data[4] is the effect speed and
data[5] is the brightness, the other way around from what the comments
said. The bytes written are unchanged, this only fixes the labels.
Victor Ferreira