Enchantment — Aura, 2{G/W} (3)
Common
Enchant creature
As long as enchanted creature is green, it gets +1/+1 and is indestructible. (Lethal damage and effects that say "destroy" don't destroy it. If its toughness is 0 or less, it's still put into its owner's graveyard.)
As long as enchanted creature is white, it gets +1/+1 and has flying.
Illus. Steven Belledin

5/1/2008: If the enchanted creature is both of the listed colors, it will get both bonuses.
5/1/2008: If an effect would simultaneously destroy Shield of the Oversoul and a green creature it's enchanting, only the Shield is destroyed.
5/1/2008: If a green creature enchanted by Shield of the Oversoul is dealt lethal damage, the creature isn't destroyed, but the damage remains on the creature. If Shield of the Oversoul stops enchanting that creature later in the turn, the creature will stop being indestructible and will be destroyed.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern