Hmmm. One of the reasons Lee is an industry standard is due to their consistent quality, also partly why they command a big price. If you are getting colour cast problems like that I can only think that either you got a bad copy, or as they say..."you're doing it wrong!"
As far as Lee, well...they are LEGENDARY for their supply problems. Not just for the Bigstopper, which took off in popularity I'd say a few years ago and made an item already produced in small numbers, incredibly hard to find. I received my copy from Robert White in the UK (link is shown earlier in the thread) about eight months after ordering. And that was because B&H, Adorama, Amazon, every US supplier I Googled didn't have it in stock during that entire time! I'm sure some did, at certain times, but with only 1 or 2 arriving in stock they would be gone instantly, so it would only be sheer luck to find one somewhere.
It has also taken me literally a couple of years to assemble the bits and pieces of filter gear I wanted for my various lens sizes, I have a one stop and a two stop ND, 105mm circular polarizer, Foundation Kit (also notoriously hard to obtain) and the low-profile rings to adapt for 72, 77, and 82mm filter rings. I had to use different suppliers and hunt them down, one by one. I would source one ring from one random supplier in the US, another in the UK - a virtual treasure hunt!
So why all the issues? Lee is a bit of a throwback company, they literally make every filter by hand in England. If you want to see a really interesting video that may
relieve a bit of the frustration of waiting forever for their products to ship, or at least answer a few questions, check out this link:
There is no Cheap Chinese off-shoring here, they are hand-dipping
each filter to dye them and then individually testing each one manually!
And this is expected to supply behemoths like B&H!
Having said that, the effort made the success of getting them all the more sweet, as well as the pleasure of using high-quality, truly handmade products with beautiful results. But if it's instant gratification one wants, better to go with a cheaper (and nearly as good) competitor.