Extra Color Palette for One Post Type

// Post type that gets the extra colors, and the colors (slug => [name, hex]).
$wpide_pt_palette_type   = 'page';
$wpide_pt_palette_colors = array(
    'wpide-campaign-red'  => array( 'Campaign red', '#dc2626' ),
    'wpide-campaign-gold' => array( 'Campaign gold', '#ca8a04' ),
);

add_filter( 'wp_theme_json_data_theme', function ( $theme_json ) use ( $wpide_pt_palette_type, $wpide_pt_palette_colors ) {
    if ( ! is_admin() ) {
        return $theme_json;
    }

    // phpcs:disable WordPress.Security.NonceVerification.Recommended
    $type = '';
    if ( ! empty( $_GET['post_type'] ) ) {
        $type = sanitize_key( $_GET['post_type'] );
    } elseif ( ! empty( $_GET['post'] ) ) {
        $type = (string) get_post_type( absint( $_GET['post'] ) );
    } elseif ( isset( $GLOBALS['pagenow'] ) && 'post-new.php' === $GLOBALS['pagenow'] ) {
        $type = 'post';
    }
    // phpcs:enable

    if ( $type !== $wpide_pt_palette_type ) {
        return $theme_json;
    }

    $data    = $theme_json->get_data();
    $palette = isset( $data['settings']['color']['palette'] ) ? (array) $data['settings']['color']['palette'] : array();
    $palette = isset( $palette['theme'] ) ? (array) $palette['theme'] : $palette;

    foreach ( $wpide_pt_palette_colors as $slug => $color ) {
        $palette[] = array( 'slug' => $slug, 'name' => $color[0], 'color' => $color[1] );
    }

    return $theme_json->update_with( array(
        'version'  => WP_Theme_JSON::LATEST_SCHEMA,
        'settings' => array( 'color' => array( 'palette' => $palette ) ),
    ) );
} );

add_action( 'wp_enqueue_scripts', function () use ( $wpide_pt_palette_type, $wpide_pt_palette_colors ) {
    if ( ! is_singular( $wpide_pt_palette_type ) ) {
        return;
    }

    $css = '';
    foreach ( $wpide_pt_palette_colors as $slug => $color ) {
        $slug = sanitize_key( $slug );
        $hex  = sanitize_hex_color( $color[1] );
        $css .= ":root{--wp--preset--color--{$slug}:{$hex};}.has-{$slug}-color{color:var(--wp--preset--color--{$slug})!important;}.has-{$slug}-background-color{background-color:var(--wp--preset--color--{$slug})!important;}.has-{$slug}-border-color{border-color:var(--wp--preset--color--{$slug})!important;}";
    }

    wp_register_style( 'wpide-pt-palette', false, array(), '1.0' );
    wp_enqueue_style( 'wpide-pt-palette' );
    wp_add_inline_style( 'wpide-pt-palette', $css );
} );