Here is a quick hint! We are going to show you for Reviews (bear in mind that this can be use for e.g. jaw grid as well)
Globally you can set these colors in Theme Options->Styling Options->Color Settings->Overlay Gradient Colors or Overlay Colors. Bear in mind that these colors are applied for each another post or page (not for some posts or pages).
So we have to use some custom css. First of all, open your browser inspector and find its ID.
Then go to Theme Options->Custom Stylesheets->Custom CSS and add there this code (in our case)
article#post-4187 .jaw-fadein { background: linear-gradient(to bottom,rgba(0,0,0,0) 0,rgba(255, 0, 0, 0.7) 100%); }
And the result