Changing bootstrap colors (varying the shades)

Would really appreciate some help!

How do you change the bootstrap colors (varying the shades) for multiple pages of a website?

For instance, I want to modify the shades of grey

Thanks

You can do so by adding the selectors to your style.css stylesheet.
Here are the docs for this: https://getbootstrap.com/docs/4.0/getting-started/theming/#color