Why was Liechtenstein not colonized If so then who colonized it?

Liechtenstein was not colonized because European countries that expanded and controlled their neighbors were called empires, which is distinct from colonization. In the case of Liechtenstein, it was conquered by the Carolingian Empire, but soon released as an independent principality within the Holy Roman Empire. This state of quasi-alliance with Austria (which was the most powerful member of the HRE), prevented direct conquest. When Napoleon disbanded the HRE, Lichtenstein fell under French indirect occupation for a few years before regaining its independence. From that point until the present Liechtenstein has been independent, save when it has been overrun in wartime.

The best answer to the question is that Liechtenstein's partial sublimation of independence by way of joining the Holy Roman Empire prevented its being outright conquered by neighboring Austria.