Some colors can be absolute bears when it comes to packing and it has to do with the amount of pigments needed to make the colors. The fluorescent colors mentioned below and the white have an inordinate amount of pigments but they're needed to get things to work however the X2 colors are hyper strong and can stand a lot of dilution without affecting the color's performance.
When I get either of the fluorescent chartreuses, white, fluorescent orange or fluorescent pink the first thing I do is to shake the heck out of them to be certain they are fully mixed. Once fully mixed in the original bottle I pour the whole nine yards into a 1/2 pint jelly jar and add raw plastic equal to the amount of original colorant to it, cover and shake the bejesus out of it again. To the original bottle I add three 5/16 stainless steel nuts then pour back enough colorant to fill the bottle within about 3/4" of the top. The nuts will be agitators when you shake the colorant and leaving the space at the top assures that they'll really have unfettered room to mix things up. The nuts are added to every bottle of colorant I own, hard packer or not. Simply cover the jars and store until needed, but they too need to be stirred or shook often to help keep things from packing. If the contents packs, use a spoon to carefully and slowly scrape the packed pigments until you can see areas on the bottom where pigment is no longer stuck there. Ideally, some sort of agitator should be put in the jars but being glass, one needs to be careful how large [heavy] and what type of material. I use the 3-4 lead sprues taken from jig molds in a couple of the jars and for the sake of comparison I have three or four marbles in a couple other jars. Both will work great so either one will work.
Some people bend appropriately sized wire to make a mixer that fits in a Dremel tool to do battle with hard packed colors, but I'd caution that if using this method, it might get messy in a hurry. Not saying it will.... could.
Again, in a perfect world, giving everything a decent shake session once a week would be ideal, but I know how time and things get in the way of that goal. In the most extreme cases, where I did not get to the product without any agitators inside before it packed down, I have cut the bottle off the packed pigment after dumping the oil in a bowl then adding the pigment and have used a drink mixer.... one of those corded kitchen utensils that have a blade and cover [cover sort of resembles a weed eater string shield] on a long stem to help re-blend everything. If you use this method, wear old clothes and do it out on the garage floor without anything nearby that can't get stuff on it. I always have extra empty yorker tops and bottles on hand to put half of the product back in with nuts and raw plastic to top off as previously mentioned then store the remainder in a glass jar.
As I brought up earlier, X2 colors, all of them, are super potent so by cutting them with an equal amount of plain old raw plastic will get you a lot of extra milage out of them with hardly any extra expense. I haven't found one color yet that suffers any potency from mixing with the raw plastic at a 50/50 ratio.
The best case scenario is that you shake the jars once a week to keep things blended well, but I know how that goes. When I want to use the colors with the nuts in them I turn the bottle upside down and squeeze the outside edges of the bottle until I feel those stainless nuts come loose with the packed pigment. I'll actually dimple the edges pretty good to do this. Once the things are loose inside just take time to shake really well, maybe a couple minutes, then use. The nuts will break things up in a snap and they further assist in the mixing.
