When did Magic the Gathering start using colors symbols for rare and uncommon cards?

[Rocket]

When did Magic start using colors symbols for rare and uncommon cards?

[Twanos]

Exodus was the first expansion.
6th Edition was the first core set.

Prior to 6th core set's didn't have any expansion symbol and prior to Exodus the expansion symbol on all cards was black

[seba1983]

or all silver as with ice age.

what portal sets had the rareity distinction ? just 3-kingdoms or 2nd age also ?