Having trouble with findViewById in Android

I have a for loop which is running through an an array of imageView ID's that correspond to imageViews in my 'Board' class. The code is below:

for (String s : chunks) {                                                   
    String possibleSquare = "s" + s.substring(2, 4);                        
    ImageView backgroundImg = (ImageView) findViewById(R.id.possibleSquare);
    backgroundImg.setBackgroundColor(Color.rgb(255, 255, 255));   

I'm getting an error with findViewById and possibleSquare, specifically that Android 'cannot resolve' either.

What am I doing wrong?