Does Prismatic Omen make it so that I can tap land for any type of mana, or does it only change the effects of spells like Corrupt ?
212.6g The basic land types are Plains, Island, Swamp, Mountain, and Forest. If an object uses the words "basic land type," it’s referring to one of these subtypes. A land with a basic land type has an intrinsic ability to produce colored mana. (See rule 406, "Mana Abilities.") The land is treated as if its text box included, ": Add [mana symbol] to your mana pool," even if the text box doesn’t actually contain text or the card has no text box. Plains produce white mana; Islands, blue; Swamps, black; Mountains, red; and Forests, green.
212.6h If an effect changes a land’s subtype to one or more of the basic land types, the land no longer has its old land type. It loses all abilities generated from its rules text and its old land types, and it gains the appropriate mana ability for each new basic land type. Note that this doesn’t remove any abilities that were granted to the land by other effects. Changing a land’s subtype doesn’t add or remove any card types (such as creature) or supertypes (such as basic, legendary, and snow) the land may have. If a land gains one or more land types in addition to its own, it keeps its land types and rules text, and it gains the new land types and mana abilities.
* Each land you control will have the land types Plains, Island, Swamp, Mountain, and Forest. They'll also have the mana ability of each basic land type (for example, Forests can tap to produce :g. They'll still have their other subtypes and abilities.