A: Trick Jarrett, Editor-in-Chief of DailyMTG.com
Up until the Innistrad block, there were only two ways for a card to be colored. First was, of course, the mana in its casting cost. Was there white mana? Then it was a white spell. Was there blue and red mana? Then it was both a blue and a red spell.
Occasionally we did spells that broke this rule. Summoner's Pact has a casting cost of but is a green spell, and so when it was originally printed it included a line in the rules text that defined the spell as a green spell.
In Innistrad block, for the rules around double-faced cards, we needed a way to easily show the color of a spell, since the backs of the cards didn't have casting costs. So when Gatstaf Shepherd transformed into Gatstaf Howler, we could easily show that even though the Howler didn't have a mana cost he still remained a green creature. To do this without using up space in the rules text, we introduced the color indicator, which is the dot you now see in the type line when you transform the Shepherd.
With this new technology, as we reprint cards that made use of the clunky rules text, we're updating them to make use of the new color indicator. This, by the way, isn't the first reprint to make use of the new color indicator. You might remember Dryad Arbor from last year's From the Vault.