You can change the Pad color by sending this SysEx message to "Arturia MiniLab mkII" MIDI output port (you may want to buy back the Minilab):
F0 00 20 6B 7F 42 02 00 10 7n cc F7
where:
n is the pad number, 0 to F, corresponding to Pad1 to Pad16
cc is the color:
00 - black
01 - red
04 - green
05 - yellow
10 - blue
11 - magenta
14 - cyan
7F - white