Could you please post your website's URL?
AdminCP > Templates > Your theme's templates > Forumbit Templates > forumbit_subforums > find the following;
{$lang->subforums}
and Change it into;
<span class="subforums_class">{$lang->subforums}</span>
Now in your theme's global.css, define the following class;
.subforums_class{
color: #F2EF04 !important;
}
It should turn the text into yellow color. You may play with the hex color code to suite your desired color