I think that the colour card test is ambiguous unless it has been agreed in advance exactly what the names of the colours are. Would "azure" be acceptable for "blue", for instance? People often disagree about colours.
Assuming that the spirits can read, would it not be better to write a different word on a number of cards and put them in an envelope, all with the backside up. The tester (Alderman) then picks a random card and takes it out so that neither he, nor the claimant (flaccon) can see it, but the spirits can have a clear view of the front side of the card. Then the card is placed on the table with the back upwards, still without having been seen by the tester or the claimant.
The claimant makes the spirit recording, and asks the spirits what card they had seen, and makes a playback which she listens to and writes down what she believes is the answer by the spirits. Then a comparison is made with the actual card.
Since this is an informal test, no number of hits and misses need be agreed upon in advance, but if the spirits can read, and the writing is clear, we would expect every single answer to be right, or allowing for the fact that flaccon may not always be able to hear what the spirits say, perhaps 3 misses out of 25 would be acceptable?
This test is easy to do, and only needs the cooperation of the spirits. We could promise the spirits that a successful test would give the support of the skeptics for a renewed contact to a bishop!