To change the colours of the instructor box, copy and paste the following into the child theme style sheet or in Divi > Theme Options > General > Custom CSS:

.llms-instructor-info .llms-instructors .llms-author {
    border-top: 4px solid #43BFB4;
}

.llms-instructor-info .llms-instructors .llms-author .avatar {
    background: #43BFB4;
    border: 4px solid #43BFB4;
}

Modify the hex codes to match your colour scheme.