Change color of “Read More” buttons on Home page

This custom CSS should work:

.hentry .link-more a {
	background-color: purple;
}

/* change the background color here if you'd like the button to be a different color on hover */
.posts .hentry:hover .link-more a {
	background-color: purple;
	color: white;
}

An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.

A custom CSS editor is also included in the Customizer as of WordPress 4.7.

As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.

I think css code should be work

Only you need to get the class of the div or link
And change the background of it in css

Thanks very much guys!

You’re welcome!