They were the same nation many years ago. Ireland couldn't locally source a good colorfast red dye and so just used what they could and ran with the result. Several washes later, this resulted in the great Italo-Irish civil war of just-pretend-I-put-a-year-here-that-I-pulled-out-of-my-butt.
What's the difference between Ireland and Italy?

Are we talking about the flag or the country? If it's the country then I think the weather must be one of the answers, they don't call it the Emerald Isle for nothing!
The flag of Eire was designed to bring the differing fasctions together. The Green of the South, the Orange to represent Protestant opinion and the White in the middle to signify peace. Dunno bout Italy though.
Ireland--
Italy--
For those of you who aren't colour blind--those are the EXACT SMAE COLOURS~!!!!!!!!!!!~!!!!!!!!!!!!