You will need to use two loops if you want a 2 dimensional array, one nested inside the other. The first loop will create the individual arrays and the second will assign the elements to each.
var mArray:Array = new Array();
for(var i:int=0; i<8; i++){
mArray[i] = new Array();
for(var k:int=0; k<8; k++){
mArray[i].push(whichever color you intend);
}
}