[KaktoR]

I guess it's the background color for WizardForm.

Try to change it using this
http://www.jrsoftware.org/ishelp/ind...etup_backcolor

For splash screen you can use isgsg.dll library (attachment)

How to use:
Add isgsg.dll to script (in [Files] section)
Add Splash.png to script (in [Files] section)

procedure ShowSplashScreen(p1:HWND;p2:AnsiString;p3,p4,p5,p6,p7:integer;p8:boolean;p9:Cardinal;p10 :integer);
    external 'ShowSplashScreen@files:isgsg.dll stdcall delayload';

procedure InitializeWizard();
  ExtractTemporaryFile('Splash.png');
  ShowSplashScreen(WizardForm.Handle,ExpandConstant('{tmp}\Splash.png'), 1000, 1000, 1000, 0, 255, True, $FFFFFF, 10);