#wpadminbar ul li#wp-admin-bar-cache-purge {
    background: white !important;
}
#wpadminbar ul li#wp-admin-bar-cache-purge a.ab-item {
    color: black;
}
#wpadminbar ul li#wp-admin-bar-cache-purge a.ab-item:hover {
    color: white;
}
#wpadminbar ul li#wp-admin-bar-cache-purge a .ab-icon:before {
    color: black;
}
#wpadminbar ul li#wp-admin-bar-cache-purge a:hover .ab-icon:before {
    color: white;
}