There are first-edition base sets from the late 1990s, Japanese exclusives, holographic "shadowless" variants, and reprints that only collectors can tell apart
Like most Pokmon cards, the value of Porygon-Z depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Unbroken Bonds)
Some things that may draw you into specific colors are: A really strong rare you're excited about Plenty of "removal" cards that can deal with your opponent's creatures A lot of playable cards in that color A good "mana curve" in that colormeaning lots of creatures of different costs Ideally, the colors you pick will have all four, but if two or three of those are true that's plenty good
Dimir Informant brings with it a new possibility for Blue decks
This Rainbow Energy captures the spirit of that by doing ten damage to the Pokemon you attach it to