You can add colors there by adding few CSS tweaks. You can find the following code example of .panel-acqa class in style.css file. Here you can add the new class which you want to create like others.
.panel-aqua > .panel-heading,
.panel-brown > .panel-heading,
.panel-tan > .panel-heading,
.panel-red > .panel-heading,
.panel-orange > .panel-heading,
.panel-green > .panel-heading {
color: #fff;
border-color: #e7eaec;
}
And the following line controls the background color. Create your new class like this.
.panel-aqua > .panel-heading {
background-color: #25b7c3;
}
I hope you’ll be doing these addition to child theme.