Light up any key, from anywhere.

import mido

MFR = [0x05, 0x30, 0x7F, 0x7F, 0x20, 0x00]
enc = lambda v: [v // 128, v % 128]

out = mido.open_output(next(n for n in mido.get_output_names()
                            if 'partykey' in n.lower()))
out.send(mido.Message('sysex', data=MFR + [0x0F, 0x01]))   # enter LED mode

def set_leds(groups):
    payload = MFR + [0x15, len(groups)]
    for rgb, keys in groups:
        payload += enc(rgb[0]) + enc(rgb[1]) + enc(rgb[2])
        payload += [len(keys)] + list(keys)
    out.send(mido.Message('sysex', data=payload))

set_leds([
    ((255, 0,   0  ), [17]),
    ((0,   255, 0  ), [18]),
    ((0,   0,   255), [19]),
])

import JZZ from 'jzz';

const MFR = [0xF0, 0x05, 0x30, 0x7F, 0x7F, 0x20, 0x00];
const enc = v => [Math.floor(v / 128), v % 128];

const engine = await JZZ();
const name = engine.info().outputs.find(p => /partykey/i.test(p.name)).name;
const out = JZZ().openMidiOut(name);

out.send([...MFR, 0x0F, 0x01, 0xF7]);   // enter LED mode

function setLEDs(groups) {
  const msg = [...MFR, 0x15, groups.length];
  for (const g of groups) {
    msg.push(...enc(g.rgb[0]), ...enc(g.rgb[1]), ...enc(g.rgb[2]));
    msg.push(g.keys.length, ...g.keys);
  }
  msg.push(0xF7);
  out.send(msg);
}

setLEDs([
  { rgb: [255, 0,   0  ], keys: [17] },
  { rgb: [0,   255, 0  ], keys: [18] },
  { rgb: [0,   0,   255], keys: [19] },
]);

import CoreMIDI

let MFR: [UInt8] = [0xF0, 0x05, 0x30, 0x7F, 0x7F, 0x20, 0x00]
func enc(_ v: UInt8) -> [UInt8] { [v / 128, v % 128] }

var client = MIDIClientRef(); var port = MIDIPortRef()
MIDIClientCreate("PK" as CFString, nil, nil, &client)
MIDIOutputPortCreate(client, "out" as CFString, &port)

var dest: MIDIEndpointRef = 0
for i in 0..<MIDIGetNumberOfDestinations() {
    let d = MIDIGetDestination(i)
    var n: Unmanaged<CFString>?
    MIDIObjectGetStringProperty(d, kMIDIPropertyName, &n)
    if ((n?.takeRetainedValue() as String?) ?? "").lowercased().contains("partykey") {
        dest = d; break
    }
}

func sendSysEx(_ data: [UInt8]) {
    var pkt = MIDIPacketList()
    let p = MIDIPacketListInit(&pkt)
    _ = MIDIPacketListAdd(&pkt, 1024, p, 0, data.count, data)
    MIDISend(port, dest, &pkt)
}

sendSysEx(MFR + [0x0F, 0x01, 0xF7])      // enter LED mode

func setLEDs(_ groups: [(rgb: (UInt8, UInt8, UInt8), keys: [UInt8])]) {
    var msg = MFR + [0x15, UInt8(groups.count)]
    for g in groups {
        msg += enc(g.rgb.0) + enc(g.rgb.1) + enc(g.rgb.2)
        msg += [UInt8(g.keys.count)] + g.keys
    }
    msg.append(0xF7)
    sendSysEx(msg)
}

setLEDs([
    (rgb: (255, 0,   0  ), keys: [17]),
    (rgb: (0,   255, 0  ), keys: [18]),
    (rgb: (0,   0,   255), keys: [19]),
])