It's a question of semantics as to whether 'conquered' means 'colonized'. The Italians were there for only five years and didn't have time or the means to enact the substantial population, infrastructure, and cultural changes that are entailed by the term "colonization".

In a comparison of similar duration and era, we don't say that France was colonized by Germany in 1940-1944.

You might be interested in some previous threads on Ethiopa and colonization:

Ethiopian Resistance to Colonization

• I've heard that Japan, Korea, Thailand and Liberia were the only countries unaffected by European colonialism. How accurate is this statement? - 5 comments, over 2 months old.
• There are some very brief summaries of these countries' histories with colonization.
• Ethiopia stayed independent during the 19th-20th C European colonization of Africa. What enabled it to stay autonomous? - 24 comments, over 1 year old.
• This thread discusses Ethiopian resistance to colonization before the Italian colonization, with the Ethiopian modernized military and centralized state being hot topics.

Modern Ethiopia

• Why is Ethiopia the way it is? - 90 comments, over 2 years old.
• This thread goes into the history of Ethiopia during the Cold War with relevant background information from the Scramble for Africa.