How can I show custom field according to taxonomy?

In your loop use has_term( $term, $taxonomy, $post ).

1. Check if the post has the term you are searching for.
2. Check if there is a value for the custom field.
3. Print the value, but don’t forget to escape it.

if ( has_term( 'blue', 'product_color', $post ) )
{
    $field = get_post_meta( $post->ID, 'field_name', TRUE );

    if ( ! empty ( $field ) )
        echo esc_html( $field );
}