Hi and welcome back!
Unlike the APC-MINI MK1, the MK2 has a different color map.
In general, for brightest LEDs, you should sent MIDI Note-On on MIDI Channel 7 instead of MIDI CH1. This is true for the matric buttons only. For the bottom and side button, continue to send on MIDI CH 1.
This posting documents the different velocities for colors and more details on the APC-MINI MK2 protocol.
White would be a velocity of 3 for the APC MINI MK1 I believe this velocity is for red (but MIDI CH 1).
Steve Caldwell
Bome Customer Care
Also available for paid consulting services: bome@sniz.biz