Anne - Just as we didn't make anything which needed to match from the flint (i.e. supposedly colourless) tank during the crisis we certainly wouldn't be trying to match any butterfly stuff made in the normal way from pots with the dodgy, variable, accidental blue from the tank! Although, as I said, cobalt blue of any depth of colour must be one of the easiest colours to control (given non-cut-price raw materials and decent lab-type balances - Sowerby blue used, I think, 4 grams of cobalt oxide per 1000 lbs of sand) the appearance of very pale colours can depend hugely on the shape and texture of the article concerned, which I'm sure you know already. One could always cut lumps from the articles and grind and polish them to the same size for comparison but the owners might not appreciate that approach.
Peejy - I am certain that no attempt was made to make matching holders for dodgy blue vases. I'm afraid it will have to be colouless or normal blue!
Adam D.