Obviously it was colonized in a very real sense by freed American slaves, but why did that stop the European powers? Was there an understanding that the USA would act as a guarantor of Liberian independence? Or was it a more ideological sense that because Liberia already had colonizers who were there on a civilizing mission (even though the colonizers weren't white), that European colonization wasn't necessary?
I've always been fascinated with the parallels between Liberia and Israel. An oppressed and persecuted people return to their "roots" but in fact become colonialists themselves.
To answer your question, yes in its early years Liberia was viewed as a colony. It was under the protection of the United States. Later the European powers tried move against it, forcing it to cede territory to them in the early 20th century. Interestingly, some natives rebelling against Amero-Liberians called for British intervention on their behalf.