How to change primary menu colour?

I am using the shapely theme for customising my site.The main thing I am struggling with it is changing the primary menu color.I have added “About Us, Gallery” sections to my primary menu.But since I have changed my background colour to black the menu texts almost looks invisible .I want to change these primary menu section colour to white.
Also I don’t have much css knowledge.So if somebody can guide me to change the primary menu colour to white it will be really helpful.
Thanks in advance.

Hi there,
Thanks for reaching out.
In reference to your question here, please provide us with a link to your site so that we can provide an accurate code for this.
I look forward to your reply.
Best Regards,