Another shortcut instead of creating an overlay is to simply use the RGB params in the screen section of the Asteroids layout file:
screen index="0" bounds x="752" y="660" width="2512" height="1884" color red = "0.1" green = "0.6" blue = "1.0" screen
I just used these numbers as an example, but you can tweak them to get the right tint of blue you need. If you need white vectors with a blue glow, this won't work.
----------------------
I have officially retired from sucking at everything I do. Life is much easier now.