General Colors

From the WP Dash, under Appearance > Theme Options > Colors, there are two color inputs that affect many of the colors in the theme:

Other Colors & Styling Changes

For areas not affected by the color settings in the Theme Options area, our general recommendation is to use the Inspector feature available in Chrome and Firefox. Just right click on an element on the page and select Inspect Element:

Then you can see the CSS that is affecting the element in question:

From there, you can copy/paste the relevant sections into your child theme or Custom CSS box and make the necessary changes. (Appearance > Theme Options > General > Custom CSS)

More info on the Chrome Inspector: https://developer.chrome.com/devtools
More info on the Firefox Inspector: https://developer.mozilla.org/en-US/docs/Tools/Page_Inspector

Page or Section Specific Changes

If you want to make changes specific to one page or just one section, you can make use of the unique IDs and unique classes.

The same as above, when you right click and select Inspect Element you'll see the source of the page which will show that each page has a unique class:

You can use that in your code like so:

.page-id-2710 h3 {color:#333}

That would change the color for all h3 tags on that one specific page.

Scrolling down you'll see that each section has its own IDs and classes that can be used in the same way:

The selected div tag ID comes from the anchor (if you are using one). The other ID and classes are all output by the meta box.