How to change this line's color?

is the website drdanieljaredsmith.com & where it says ‘I’d like to change the color of the line below this title…’
Add this to your child theme

.modline-outer {
   border-bottom: 1px solid #78A5B6;(change #78A5B6  to your color)
    border-top: 1px solid #78A5B6;(change #78A5B6 to your color)
    height: 2px; (can be left out in child theme)
    margin-bottom: 18px; (can be left out in child theme)
}
.modline-inner {
    background-color: #78A5B6;(change #78A5B6 to your color)
    height: 2px; (can be left out in child theme)
    width: 25%; (can be left out in child theme)

}

To remove it just add
.modline-outer {
display:none;
}
.modline-inner {
display:none;
]