It's easy, you roll a normal spellcraft. "With your spellcraft check of 28, you recognize the bluish mist surrounding the enemy mage as a chill shield." When the fighter sees this, unless he is clued in by someone with a good spellcraft, he has zero chance of metagaming and, more importantly, the veteran players will find it much more interesting. Heck, I wouldn't even bother mentioned green flames because I don't even need a spellcraft check for that. Requiring the use of spellcraft for spellcraft rolls makes my suggestion very consistent.
In effect, what you're suggesting is that the players use their own knowledge of the descriptions of spells to do spellcraft and not their spellcraft roll.
I agree that they may have an in-game effect and, depending on the nature of that effect I would recommend caution. This is why I caveated my comment with "little or no effect". So, as DM you either restrict the flavor appropriately, or you just plain decide not to let it have an in-game effect.
That's exactly my point. Unless you have sufficient spellcraft, you shouldn't know what the spell is. You shouldn't let metagame knowledge when you once played an archmage up to 20th level affect what your 4th-level fighter would know.