TO customize pega blue screen error page we need to update Status.jsp 

Where we can find this file.

I had Installed Personal edition in my D drive , Open the below path to get Status.jsp

D:\Syed\Syed\Pega8.3\PRPCPersonalEdition\tomcat\webapps\prweb\diagnostic/Status.jsp

Updated BackgroundColor

body {       background:linear-gradient(-150deg,#125876 0%,#1F2555 20%);       background-repeat: no-repeat;

}

To Update the Desired logo, we can update Pega svg logo

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 311 68"><title>Pega with flying horse logo</title><path fill="#fff" d="M78.42 9.8a45........"/></svg>     <div class='info'><%= new Date(System.currentTimeMillis()) %>. <%= sETierVersion %></div>     <div class='message'><%= sMessage %></div>     <div class='details'>         <div><label>Status:</label><%= sStatus %></div>         <div><label>Operator:</label><%= sUserName %></div>         <div><label>Node:</label><%= sRequestorID %></div>    </div>

Please refer attached screen shot for  more reference.