Reporting Services dynamic formatting is controlled by expressions. The SWITCH function is one method of implementing logic inside an expression (like TSQL's CASE statement).
To quote Books Online , SWITCH -
' Evaluates a list of expressions, and returns the value associated with the first condition that returns TRUE. Switch can have one or more condition/value pairs. 'So applying this in an expression to the BackgroundColor property of a cell >
=Switch(First(Fields!Elapsed_Minutes.Value) < 30, "Green", First(Fields!Elapsed_Minutes.Value) < 60, "Yellow", First(Fields!Elapsed_Minutes.Value) >= 60, "Red", 1=1, "Transparent")
Breaking this example down, it uses the Elapsed_Minutes column and uses GREEN for values less than 30 minutes, YELLOW for values less than 60 minutes and RED for values over 60.
The 1=1 argument becomes true if none of the previous arguments are satisfied i.e Elapsed_Minutes is NULL / not present.