If you need to edit the fade in effect of the Page Title background image to fit your website style, please go to Customizer > Global styles > Accent Colors and edit Accent 6.

This change will affect some other elements of your design, so in some occasions you'll need to edit particularly this effect, without changing the global accent color. 

In that case please add the code below to Customizer > Additional CSS (check this guide for more details)

#sub-header .text-shadow {
  background: red;