def METHOD_NAME(RGB_true, RGB_pred, alpha_mask):
    """Computes foreground reconstruction L1 loss by using only positive alpha
        mask values.
    # Arguments
        RGB_true: Tensor [batch, H, W, 3]. True RGB label values.
        RGB_pred: Tensor [batch, H, W, 3]. Predicted RGB values.
        alpha_mask: Tensor [batch, H, W, 1]. True normalized alpha mask values.
    # Returns
        Tensor [batch, H, W, 3] with foreground loss values.
    """
    foreground_true = RGB_true * alpha_mask
    foreground_pred = RGB_pred * alpha_mask
    foreground_loss = tf.abs(foreground_true - foreground_pred)
    return foreground_loss