A scheme can hold only one page style per class (per kind of folder and per kind of topic). This is fine as long as all your documents appear in a specific house style or only in a few of them.
But what if many of your documents require a specific look and feel? Suppose, for example, we would like to give each of our ‘Bird’ folders a background other than the ‘Plant’ folders background, how would we do this?
In such a case, we have to work with specific page styles instead of generic page styles, but the principle is the same. However, a specific page style is not part of a scheme and is always attached (manually or automatically) to one or more specific folders or topics.
A scheme can be considered a bunch of ‘fall back’ page styles. If a folder or a topic has no specific page style attached then it is automatically displayed according to its generic counterpart in a scheme.