The CSS rule that is setting the color of the site title, which you referred to being on line #58 of index.php (which is actually shown as line #60 in your screenshot), I think, is generated from the WordPress customizer – Appearance -> Customize from within your admin area.
The Chrome element inspector isn’t referring directly to the index.php file (it can’t read the PHP files, only the generated/printed HTML). It’s actually referring to the HTML page that’s generated from the sites PHP code – you can view this, by right clicking and choosing View Source or press Ctrl-U/Cmd-U in Google Chrome.
In order to change the color of the site title, you should be able to change this via Appearance -> Customize in your sites admin.
If you’d like to do more advanced customisation of the site title, you would need to target this in the sites style.css file. I would, however, recommend doing any CSS customisation in a Child Theme, if you’re not doing so already (which I get the impression you’re not)…
It’s important to use Child Themes because if your theme is updated any customisation to the code will be lost. With a Child Theme, your customisations will be maintained.
If you’ve already made changes to the sites style.css file to alter anything (other than the color or any other setting that’s generated from the ‘Customizer’) and they aren’t updating on the site, then it’s probably a browser cache issue. In this case, clear your browsers cache or try viewing the site in another browser.