Here is a quick & dirty test of my "heavy" ND filters, courtesy of my neighbor's front yard... Now these exposures are only in the 1-second range so they're not long enough to test for "IR bleed-through," but simply demonstrate the different colors associated with these heavy ND filters. As you can see, the Haida filter appears to be the most color-neutral in this situation, and the B+W appears to be a reasonably close second-place. While the (second place) B+W filter doesn't appear to have a heavy color cast, it can be real hell to correct in a long exposure. The Haida is a new purchase for me so I don't yet have any experience color-correcting it when used in very long exposures. Ironically, the widely popular Lee Big Stopper easily has the heaviest (blue) color cast, but I find it to be a piece of cake to correct in post! Go figure... Maybe the blue color cast filters out some of the "IR bleed-through," I don't know... BTW, by "long exposures" I'm talking 2, 4, & 8 minutes.