Adafruit Bi-Color 8x8 Matrix

Typical, write a post and find the answer :) Turns out I needed some other methods to be called first to setup the device. The following works:

// Variables
var address = 0x70;
var displaybuffer = new Uint16Array(8);

var LED_OFF = 0;
var LED_RED = 1;
var LED_YELLOW = 2;
var LED_GREEN = 3;

var HT16K33_BLINK_CMD = 0x80;
var HT16K33_BLINK_DISPLAYON = 0x01;
var HT16K33_BLINK_OFF = 0;
var HT16K33_BLINK_2HZ  = 1;
var HT16K33_BLINK_HALFHZ  = 3;

// Setup I2C
I2C1.setup({ scl: B6, sda: B7 });

function clearDisplay(){
 for (var i=0; i<8; i++) {
    displaybuffer[i] = 0;
 } 
}

function setBrightness(lvl) {
  if (lvl > 15) {
    lvl = 15;
  }
  I2C1.writeTo(address, 0xE0 | lvl);
}

function blinkRate(b) {
  if (b > 3) b = 0; // turn off if not sure
  I2C1.writeTo(address, HT16K33_BLINK_CMD | HT16K33_BLINK_DISPLAYON | (b << 1));
}

function drawPixel(x,y,color){
  
  if(x < 4){
    x += 4;
  } else {
    x -= 4;
  }

  if(y < 4){
    y += 4;
  } else {
    y -= 4;
  }
  
  if (color == LED_GREEN) {
    displaybuffer[y] |= 1 << x;
  } else if (color == LED_RED) {
    displaybuffer[y] |= 1 << (x+8);
  } else if (color == LED_YELLOW) {
    displaybuffer[y] |= (1 << (x+8)) | (1 << x);
  } else if (color == LED_OFF) {
    displaybuffer[y] &= ~(1 << x) & ~(1 << (x+8));
  }
  
}

function writeDisplay(){
  var tmp = new Uint8Array(17);
  tmp[0] = 0x00;
  for (var i=0; i<16; i+=2) {
    tmp[i+1] = displaybuffer[i/2] & 0xFF;
    tmp[i+2] = displaybuffer[i/2] >> 8; 
  }
  console.log(tmp);
  I2C1.writeTo(address, tmp);
}

// Turn on oscillator
I2C1.writeTo(address, 0x21);

// Set blink rate
blinkRate(HT16K33_BLINK_OFF);

// Set to full brightness
setBrightness(15);

// Draw pixels
drawPixel(0,0,LED_GREEN);
drawPixel(1,1,LED_RED);
drawPixel(2,2,LED_YELLOW);

// Update display
writeDisplay();