There are a lot of factors a person has to work around on some colors and white is not an exception. In fact white can be the worst color to work with.
Starting with white colorants themselves, there are many on the market. Some are less potent and require three or four times the drops of others. The thinner the colorant, the easier the learning curve. X2 colorants are super heavy, both in color concentration and in pigment load, and call for very few drops to make a nice solid white in a cup of plastic. The titanium white pigment in the X2 color is very heavy and dense by nature and will in fact absorb heat making it harder to figure out. When I do white using the X2 colorant I make sure its mixed well then , using a clean, empty bottle with a yorker cap, I add 1/2 bottle of the colorant and add the same amount of raw plastic and mix it by shaking the heck out of it. This blend will make your white with the same drop count as the X2 but has 1.2 of the pigment load so the pigment heating issue is roughly half that of the full strength product. Done as such its still much stronger than MF and Lureworks stuff, just easier to work with in getting rid of heating issues.
On the skillet idea.....I have a heat bed made from a square electric skillet that has cavities in silica sand for five 8 ounce pyrex desert cups. Shown here, is an empty cup except for a 4" Ripper and seen with a tape for size reference.
I mixed the sand with some water and elmers glue, then laid a bed of the sand mixture about 1/2" thick on the bottom of the skillets then spaced the five cups on the sand bed and filled in around the cups with more sand until the sand level was about 1/4" below the top of the lip of the cups. This was allowed to dry for several days before removing the cups to finish drying a few days longer yet. The cups were greased with Crisco before the sand was packed around them and they released right away when given a slight turn for the drying finish. I filled the cups with cooking oil and turned the heat on low, gradually increasing it until I hit a temp of 320 degrees in each cup, then I super-glued the rheostat in place. The oil got dumped. This gave me a hot bed that when plugged in went up to the 320 degrees without having to mess with constantly checking temps and cups that did not get filled with hot plastic from the microwave had junk plastic plugs in them so heating stayed constant. The junk plugs came out if the cups were needed. If you're doing a bunch of colors, this system works well as long as you're not doing huge baits that constantly suck up the plastic in the cups. It works really well when doing split colors as the different plastics stay at a usable heat level. I make small baits primarily and the system works great for this. Probably not super practical for big runs.
If you cook with a microwave, cut a corrugated cardboard palette to size that fits on the glass tray or rotisserie of the unit. Keep that on the tray all the time as it offers a buffer that will help eliminate hot spots inside the cabinet of the microwave and they all have these hot spots. It has to be corrugated cardboard, not the thin stuff used in gift boxes. This can go a long way in assuring even heating, which is a headache when doing light and clear colors.
Use the thermometer. Stop the heating on the initial cooking, a few degrees under the 350 degrees and let the cup rest a half a minute. Check the temp and you'll find that the plastic has come up several degrees. Cooking food shows this occurrence and plastic is no different. And keep in mind that heavy, dense colors such as white, will heat higher longer after coming from the oven....often enough to start the burning process slightly and once this happens its too late to start seeking a use for it if you want a clean color on re-heats or even the initial cook. You won't know any of this is taking place by dipping your finger in what you're cooking. Use the thermometer.
Not all plastics are created equal. The different weights [soft, medium, firm] in a specific brand of plastic will have different heating characteristics and a person has to figure out how long is enough or too long to push the plastic in a light color. It all comes with practical experience and there is no standardized worksheet that answers it all....only some suggested temps and cook times. When I am doing white I cook in much sorter bursts and stir the heck out of it at each stop. I use stabilizer at the initial cook but before I even use the white for an injection I add and stir in more stabilizer so when I have to re-heat, again in short bursts, the stabilizer is already incorporated in the plastic. I do this when I am ready to inject every time I use a re-heated white. On clear plastic I don't add any hi-lite or glitter until the plastic is at the 350 degrees and the stabilizer goes in again when I add these components if a re-heat is planned. For me the Essential series plastic is the most forgiving plastic I have used, but like all plastics, one has to "learn" it, then learn the colors. Shortcuts don't work so well and usually lead people back to this point or to pissing and moaning about bad products when in fact its operator error. Slow down, take lots of notes, USE THE THERMOMETER, and understand that all colors except for maybe black have a working life and once that threshold has been met, then black is your best option for future use.