Your basing your estimation of its worth on the fact that its sigil. What is sigil, its a combination of blue and purple, then lightened almost 100%. If I go and dye an aof say a neon green as I mentioned before, does that make it rare? Should I be able to sell it for 45m? The answer is NO, its just another color, b/c if it was the case that you could, the people who do own these dye tubs would've already capitalized on the idea.
It's not that this AOF wouldn't be worth more, if there wasn't a way to reproduce it so easily. The simple fact that it can be reproduced is what devalues it. Whether or not the entire population of UO has access to a neon dye tub, doesnt really matter b/c it only takes one person to be able to make more, and more and more. Would it be fair to sell the item to someone for an elevated price, when as I also said before, someone could come along the next day and flood the market with it? If you know that its a possibility that the item you consider rare can be reproduced so simply, then no it wouldn't be fair to sell it for an exagerated price.
I'm sure you wouldnt appreciate buying an item for roughly double its worth b/c of what you consider a unique color only to find out that its not unique at all, and that someone could easily make more.