GUI - update startup h1 colour to match theme

Author: samaaron

app/gui/qt/html/startup.html

@@ -4,7 +4,7 @@
     <center>
       <img src=":/images/logo.png" height="214dx" width="262dx"/>
 
-      <p style="font-size:50dx;color: white;background-color: #99004A;">Welcome!</p>
+      <p style="font-size:50dx;color: white;background-color: deeppink;">Welcome!</p>
 
       <p>
         This is Sonic Pi<br/>