Be able to change theme text colours without digging into code

Hello,

Sorry if this has already been answered somewhere, I searched but didn’t have much luck.

What I’m looking at doing is making a child theme for ‘Zuki’
https://zukidemo.wordpress.com

I’m designing a blog to accompany a quarterly self-published magazine for a client, and the magazine has a ‘feature accent colour’ each issue. Ideally, I’d want to blog to reflect this, each time a new issue is released.

I would want to accent things like the titles of widgets along the sidebar and in the footer, the link / rollover colour, post title colour etc. I would also want to change the colour of the social media buttons at the very bottom (but realise these probably need to be re-uploaded).

Does anyone have any suggestions as for how to go about this in a user-friendly way, so ideally the client could just enter hex codes provided by myself into a plugin or widget? I don’t want to have to go digging through various sections of code after every issue gets released.

Hopefully what I’m trying to achieve is clear enough, and someone has an idea for me.

Thanks for your time,
Jordan