The statement, "Generally, hyphenate between two or more adjectives when they come before a noun and act as a single idea" is True.
What is the true statement?
It is a rule that when two or more adjectives come before a noun and also behave as a single idea, you should hyphenate them. This is commonly known as a compound adjective because of its nature. An example can be seen in the following statement where you would say "a well-dressed man" and not "a well dressed man".
There are some exceptions to this rule as seen in the following adjectives; A red book. Here, the adjectives are not considered to be a single idea.