In functions.php add

Register color picker in customizer

//Customize Appearance Options
function custom_colorpicker_register( $wp_customize ) {

    // Add Setting
    $wp_customize->add_setting('link_color', array(
        'default' => '#ff9900',
        'transport' => 'refresh',
    ));

    $wp_customize->add_setting('btn_color', array(
        'default' => '#ff0000',
        'transport' => 'refresh',
    ));

    $wp_customize->add_setting('btn_hover_color', array(
        'default' => '#00ff00',
        'transport' => 'refresh',
    ));

    // Add Section
    $wp_customize->add_section('standard_colors', array(
        'title' => __('Standard Colors', 'ColorPickerOptions'),
        'priority' => 30,
    ));

    // Add Settings to Section
    $wp_customize->add_control( new WP_Customize_Color_Control( $wp_customize, 'link_color_control', array(
        'label' => __('Link Color', 'ColorPickerOptions'),
        'section' => 'standard_colors',
        'settings' => 'link_color',
    ) ) );

    $wp_customize->add_control( new WP_Customize_Color_Control( $wp_customize, 'btn_color_control', array(
        'label' => __('Button Color', 'ColorPickerOptions'),
        'section' => 'standard_colors',
        'settings' => 'btn_color',
    ) ) );

    $wp_customize->add_control( new WP_Customize_Color_Control( $wp_customize, 'btn_hover_color_control', array(
        'label' => __('Button Hover Color', 'ColorPickerOptions'),
        'section' => 'standard_colors',
        'settings' => 'btn_hover_color',
    ) ) );

}
add_action('customize_register', 'custom_colorpicker_register');

Change values related to color picker

<?php
    // Output Customize CSS
    function custom_colorpicker_css() { 
?>

    <style type="text/css">

        a{
            color: <?php echo get_theme_mod('link_color'); ?>;
        }

        button {
            background-color: <?php echo get_theme_mod('btn_color'); ?>;
        }

        button:hover {
            background-color: <?php echo get_theme_mod('btn_hover_color'); ?>;
        }

    </style>

<?php }
add_action('wp_head', 'custom_colorpicker_css'); 
?>