Hello Lisa,
the plugin automatically works for normal WordPress posts/pages.
You seem to have used a very sophisticated portfolio theme and/or plugin? You’d have to edit your theme to use a custom filter wherever you want to display a placeholder. Here is an example for post thumbnails:
$image = get_the_post_thumbnail( $post_id );
$image = apply_filters( 'dominant_colors', $image, get_post_thumbnail_id ( $post_id ) );
echo $image;
This is explained in the FAQ section of my plugin.
Also I do think your theme/plugin has its own lazy-loading technique, which is why the images are faded in. Two lazy-loading solutions are bound to clash, unfortunately.
