It's a bit confusing, but there are multiple versions of the purple, orange, yellow, and brown dragons.
The brown dragon in issue #38 is forest-dwelling, has a faerie fire breath weapon, an electricity breath weapon, and the ability to take the form of small animals.
The orange dragon in issue #38 has a color spray breath weapon and the chameleon-like ability to mimic a chromatic or metallic dragon.
The yellow dragon in issue #38 has blinding gas and disease cloud breath weapon and the is fond of illusions.
The purple, orange, and yellow dragons that appeared in issue #65 were updated in issue #248, eventually ending up in Dragon Compendium Vol. 1.
Gaumahavi, the "Greater Purple Dragon" from FRA 1-3 has nothing in common with other purple dragons save for its color. We've converted that one and added it to the CC.
The brown dragon that originally appeared in Old Empires and ended up in the Monstrous Manual differs from the Dragon Magazine versions. Its 3e stats are in Monsters of Faerun.
The yellow dragon that originally appeared in the 2e Draconomicon and ended up in the Monstrous Manual differs from the Dragon Magazine versions. We've converted it and added to the CC as well.