<option name="chapter" style="color: <?=color?>" class="user-chapters" ><?=name?></option>
// convert array to apopriate form
$name_colors = array_combine(
array_values($arr['name']),
array_values($arr['color']),
);
// print select options
foreach($name_colors as $name=>$color) {
printf('<option name="chapter" style="color:%s" class="user-chapters" >%s</option>'.PHP_EOL, $color, $name);
}