From the developer?s web site (where only the most recent version, for
macOS, is offered):

> f.lux makes the color of your computer's display adapt to the time
> of day, warm at night and like sunlight during the day.
>
> f.lux makes your computer screen look like the room you're in, all
> the time. When the sun sets, it makes your computer look like your
> indoor lights. In the morning, it makes things look like sunlight
> again.
>
> Tell f.lux what kind of lighting you have, and where you live. Then
> forget about it. f.lux will do the rest, automatically.

f.lux (pronounced ?flux?) runs in the background as a Login Item.

NOTE: This will not work within an emulated or virtual installation of
OS X. f.lux requires access to the hardware displays associated with
the primary system to adjust the colour temperature.

Compatibility
Architecture: PPC x86 (Intel:Mac)

f.lux 11 (PPC): PPC (10.4+)
f.lux 11 (UB): Universal Binary (10.4 to 10.6)
f.lux 36.6 (SL): Intel (up to 10.6)