Never Fear, The Customizer Is Here! [WordCamp Sunshine Coast] demo code

add_control.php

$wp_customize->add_control( new WP_Customize_Color_Control( $wp_customize, 'wordcampsc_link_colour', array(
    'label' => __( 'Link Colour', 'wordcampsc' ),
    'section' => 'colors',
) ) );

add_partial.php

$wp_customize->selective_refresh->add_partial( 'wordcampsc_link_colour', array( 
    'selector' => '#wordcampsc_customize_styles', 
    'render_callback' => function() { 
        echo 'a{color:' . get_theme_mod( 'wordcampsc_link_colour', '' ) . '};'; 
    },
) );

add_setting.php

$wp_customize->add_setting( 'wordcampsc_link_colour', array(
    'type' => 'theme_mod',
    'default' => '#337ab7',
    'transport' => 'postMessage',
    'sanitize_callback' => 'sanitize_hex_color',
) );

customizer_register.php

add_action( 'customize_register', 'wordcampsc_customize_register' );

function wordcampsc_customize_register( WP_Customize_Manager $wp_customize ) {
    // Settings etc go here
}

dry.php

function wordcampsc_customize_style_output() {
    echo 'a{color:' . get_theme_mod( 'wordcampsc_link_colour', '' ) . '};';
}

duplicate_output.php

$wp_customize->selective_refresh->add_partial( 'wordcampsc_link_colour', array(
    'selector' => '#wordcampsc_customize_styles',
    'render_callback' => function() {
        echo 'a{color:' . get_theme_mod( 'wordcampsc_link_colour', '' ) . '};';
    },
) );

function wordcampsc_customize_styles() {
    echo '<style id="wordcampsc_customize_styles">';
    echo 'a{color:' . get_theme_mod( 'wordcampsc_link_colour', '' ) . '};';
    echo '</style>'; 
}

functions.php

add_action( 'customize_register', 'wordcampsc_customize_register' );

function wordcampsc_customize_register( WP_Customize_Manager $wp_customize ) {
    $wp_customize->add_setting( 'wordcampsc_link_colour', array(
        'type' => 'theme_mod',
        'capability' => 'edit_theme_options',
        'default' => '#337ab7',
        'transport' => 'postMessage',
        'sanitize_callback' => 'sanitize_hex_color',
    ) );

    $wp_customize->add_control( new WP_Customize_Color_Control( $wp_customize, 'wordcampsc_link_colour', array(
        'label' => __( 'Link Colour', 'wordcampsc' ),
        'section' => 'colors',
    ) ) );

    if( isset( $wp_customize->selective_refresh ) ) {
        $wp_customize->selective_refresh->add_partial( 'wordcampsc_link_colour', array(
            'selector' => '#wordcampsc_customize_styles',
            'render_callback' => function() {
                wordcampsc_customize_style_output();
            },
        ) );
    } else {
        wp_enqueue_script( 'wordcampsc_customizer', get_template_directory_uri() . '/customizer.js', array( 'customize-preview' ), NULL, true );
    }
}

add_action( 'wp_head', 'wordcampsc_customize_styles' );

function wordcampsc_customize_styles() {
    echo '<style id="wordcampsc_customize_styles">';
    wordcampsc_customize_style_output();
    echo '</style>';
}

function wordcampsc_customize_style_output() {
   echo 'a{color:' . get_theme_mod( 'wordcampsc_link_colour', '' ) . '};'; 
}

selective_refresh_fallback.php

if ( isset( $wp_customize->selective_refresh ) ) {
    $wp_customize->selective_refresh->add_partial( 'wordcampsc_link_colour', array(
        'selector' => '#wordcampsc_customize_styles',
        'render_callback' => function() {
            echo 'a{color:' . get_theme_mod( 'wordcampsc_link_colour', '' ) . '};';
        },
    ) );
} else {
    wp_enqueue_script( 'wordcampsc_customizer', get_template_directory_uri() . '/customizer.js', array(), NULL, true );
}

wp_head.php

add_action( 'wp_head', 'wordcampsc_customize_styles' );

function wordcampsc_customize_styles() {
    echo '<style id="wordcampsc_customize_styles">';
    echo 'a{color:' . get_theme_mod( 'wordcampsc_link_colour', '' ) . '};';
    echo '</style>'; 
}