Hi,
First you can modify the CSS file directly in HikaShop in order to add rules.
www.hikashop.com/en/support/documentation/faq.html#css
After that, your menu (with id 158) have some options configured that you can changed in the backend in: HikaShop > Content Menu
By editing the menu with the id 158, you would found the appropriated color option.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.