Very basic question about styles/themes and how they are implemented

[stardotstar]

Hi all,

I must say that until now I have been sharpening my skills with mods and hacks for my boards in their more or less default livery. I have played around with changing the gradient images and the colours for the elements but never gone about installing a new style because when I look at the packages that they ship there appears to be a lot of differences when it comes to how existing hacks and products will work.

I want to offer my users about three styles and a heavy and light version of each. The idea is that users with low bandwidth and slow internet connections can choose the light version of a theme that they like and it will serve up smaller graphic elements, text advertising rather than images and so on.

I want to offer the following on the theme of my site "arcHELI"

arcGREY - cool greys and refined carbon fiber look
arcDARK - black theme with some neon effects
arcBLUE - clean and bright variation of the classic vB blue style
arcCLASSIC - for the purists and those who don't want things to change.

Each style will then be duplicated with the "light" version available:
arcGREYlight and so forth...

I have found some wonderful graphics here, buttons and styles but still don't quite understand the difference between these more full blown skins and a vB theme that can just be added and replaces all the values of the existing templates with simply a different colour and button, widget theme. Does that make sense?

I am reading around here and studying the way it works but wonder if I have got the concept screwed up somehow?

Are there themes which plug in and simply replicate the way that the default one works so that colours and appearances can be changed without effecting the edits to the templates and products?

Will