If you guys are still up in the air about this I can shed a little light. (Disclaimer this has already been said in the post or alluded to, but has been somewhat ignored)
This was a common question that cropped up in the league that I judge for, along with a 'why does it work?'.
With a Politoad and a Celebi-EX on the field a Poliwrath can use the attack of it's previous evolutions without needing to pay for the colourless requirements. The same applies for Poliwhirl.
Politoed can use the attacks of it's previous stages with the Celebi-EX in play, however it will have to pay all costs (including colourless requirements).
Let's break it down.
Celebi-EX
Ability: Time Recall
Each of your evolved Pokémon can use any attack from its previous Evolutions. (You still need the necessary Energy to use each attack.)
Politoed
Ability: King's Song
Ignore all Colorless Energy in the attack cost of each of your Poliwag, Poliwhirl, and Poliwrath's attacks.
Celebi-EX states that each of your evolved Pokemon can use its lower stage attacks so long as you meet the energy requirements. So far so good. It should be noted that this text means that the highest stage Pokemon is the one using the attack. You are not electing to attack with a lower stage, but have the highest stage Pokemon attack with something that it would not normally have access to from one of its lower stages (in this case either a Poliwag/whirl).
The Ability 'King's Song' only accounts for Wag, Whirl and Wrath, removing any colourless energy requirements to attack. It does not remove the colourless requirement for Politoed itself as it is not included in the ability.
A Poliwrath that attacks using Finishing Blow (Poliwhirl's attack) is the one in possession of the attack. Poliwrath is accounted for in the text of King's Song, and as such is able to use the attack without requiring any energy. Similarly, a Politoed attacking using Finishing Blow (Poliwhirl's attack) is the one in possession of the attack. However, Politoed is not accounted for in the text of its own ability, King's Song, and as such is required to pay the full cost of the attack (three colourless energy).
Hope this helps, and sorry if that came across as patronising, that wasn't my intention.
Cheers,
Mithos