When application is started for short moment it shows full white background regardless what color was set in ZINC Builder "Background Color" properties in "Window" panel (the default values are red from loaded sources flash movie in ZINC Builder).
The time during which white background is shown has different length. It is noticabe shorter in executable created with licensed version of plugin - but it is still noticable to user.

To recreate issue compile provided sample flash movie and ZINC Builder project. It sets application window background (Background Color) to black (000000).

As work-around:
#1
in ZINC Builder set "Visible" property of given window to "False"

#2
in your code:

(AS3 version):

// (AS3 example)
import mdm.*;
//
function initApp():void
{
// on startup initialize app then in ZINC runtime show main form
if(mdm.Application.filename) mdm.Forms.thisForm.show();
};
//
mdm.Application.init(this, initApp);


(AS2 version)
function initApp():Void
{
// initialize and then
if(mdm.Application.filename) mdm.Forms.thisForm.show();
};
//
setTimeout(initApp, 0);