Ok that was fun.
var socket = new Firebase("https://pixelpals-server.firebaseio.com/public");
var w = 150;
var h = 120;
var randColor = function(){
return '#'+Math.floor(Math.random()*16777215).toString(16);
};
for(var i = 0 ; i < h; i++){
for(var j = 0 ; j < w ; j++){
socket.child(i*w + j).set(i%2 ? randColor() : '#000');
}
}