Populate ACF select field's choices dynamically

functions.php

<?php

function acf_load_color_scheme_field_options( $field ) {
	$field['choices'] = array();

	$options = fetch_my_choises(); // Fetch your choises from somewhere

	if ( is_array( $options ) ) {
		foreach ( $options as $option ) {
			$field['choices'][ $option ] = $option;
		}
	}

	return $field;
}

add_filter( 'acf/load_field/name=color_scheme', 'acf_load_color_scheme_field_options' );