Spectral Procession — ruling 1

If an effect reduces the cost to cast a spell by an amount of generic mana, it applies to a monocolored hybrid spell only if you've chosen a method of paying for it that includes generic mana.

Spectral Procession — ruling 2

A card with a monocolored hybrid mana symbol in its mana cost is each of the colors that appears in its mana cost, regardless of what mana was spent to cast it. Thus, Spectral Procession is white even if you spend six blue mana to cast it.

Spectral Procession — ruling 3

A card with monocolored hybrid mana symbols in its mana cost has a mana value equal to the highest possible cost it could be cast for. Its mana value never changes. Thus, Spectral Procession has a mana value of 6, even if you spend {W}{W}{W} to cast it.

Spectral Procession — ruling 4

If a cost includes more than one monocolored hybrid mana symbol, you can choose a different way to pay for each symbol. For example, you can pay for Spectral Procession by spending {W}{W}{W}, {2}{W}{W}, {4}{W}, or {6}.

Spectral Procession : règles, fonctionnement et interactions (MTG)

Spectral Procession is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Create three 1/1 white Spirit creature tokens with flying.

How it works : Spectral Procession

Original English text — Wizards of the Coast / Scryfall

#1May 1, 2008· Wizards of the Coast
If an effect reduces the cost to cast a spell by an amount of generic mana, it applies to a monocolored hybrid spell only if you've chosen a method of paying for it that includes generic mana.
No other card is named in this ruling.
#2May 1, 2008· Wizards of the Coast
A card with a monocolored hybrid mana symbol in its mana cost is each of the colors that appears in its mana cost, regardless of what mana was spent to cast it. Thus, Spectral Procession is white even if you spend six blue mana to cast it.
No other card is named in this ruling.
#3May 1, 2008· Wizards of the Coast
A card with monocolored hybrid mana symbols in its mana cost has a mana value equal to the highest possible cost it could be cast for. Its mana value never changes. Thus, Spectral Procession has a mana value of 6, even if you spend to cast it.
No other card is named in this ruling.
#4May 1, 2008· Wizards of the Coast
If a cost includes more than one monocolored hybrid mana symbol, you can choose a different way to pay for each symbol. For example, you can pay for Spectral Procession by spending , , , or .
No other card is named in this ruling.