Why color contrast is important and example of current online companies using it?

Can someone give me examples of color contrast for accessibility which big companies websites use?

I am only able to find 2 live website examples

https://www.smashingmagazine.com/?source=post_page---------------------------

https://turbotax.intuit.com/

I am doing toggle switch contrast switch for my e-commerce website but was not able to find any other e-commerce website doing so.

Can someone give me a reference to this color contrast which other websites are using it.