Quantifying the observable effects of Type 3 civilisations

Neat ! Weirdly the link instantly closes for me on Windows, but works under Linux.

With the Sunscreen computer program, we can also figure out what would happen if the aliens are more thrifty when building their megastructures. What would happen if they could cloak stars dimmer than a thousand Suns? Most galaxies roughly fall into two classes: blue galaxies that are still making stars, and red ones where only old stars still survive. In blue galaxies, most of the light comes from blue "dwarf" stars, and the brightest of these are the most blue. So if aliens could cloak all stars fainter than 1,000 Suns, the galaxy would appear bluer than most galaxies. In red galaxies, most of the light comes from red giants, and the brightest of these are also the reddest. Cloaking the fainter red giants makes these galaxies redder, redder than natural galaxies.

http://104.197.48.230/sunscreen/