How do I change the color of the "read more" button?

Hi,
That it is an background image and is coming from the demo with custom css
If you want you can use this code to change the color ->
.td-craft-ideas .td-read-more a, .td-craft-ideas .more-link-wrap a {
background-color: blue!important;
background-image: none;
}
The custom css needs to be set in the theme panel> custom code> custom css.
Now, in case that you want to set another background image, then you can try this custom code:
.td-craft-ideas .td-read-more a, .td-craft-ideas .more-link-wrap a {
background-color: transparent !important;
background-image: url(images/read-more-bg.png);
color: #fff !important;
}
I hope this will help you!