To make sure that they get along, use skinks of a similar size and species. Enclosures can have several females, but males will tend to compete with one another. As a result it's best to give new skinks a trial run to see if they get along with the other skinks before moving them in permanently.
The difference is that a skylight filter is a basic colour correction filter with a slight magenta tint which has a similar effect on skies as a UV filter (which cuts out part of the spectrum), which is neutral coloured.
Filters for flashlights are developed and designed to extend the opportunities of usage and in fact make your device multifunctional and more efficient. Thus applying diffusors you get a wider beam that covers large area and provides perfect light for camping lighting and indoor usage.