Stabilizer has no "standard" measured amount. You have to use it in batches to find out how much is enough. In 4 ounces of plastic and making white I'd say maybe 25 drops from the Yorker cap to start. Add it to the raw plastic with the colorant and stir the heck out of it so it gets fully involved before the heat hits it.
I'm going to assume you are using a thermometer to determine the plastic temp. If you are not using a digital probe type of thermometer you maybe won't get anywhere real fast with the browning. Bottom line....get and use a thermometer if you haven't got one.
White has a huge amount of pigment in it and those pigments heat at different rates than other colors and the pigments themselves allow the plastic to continue cooking AFTER its been removed from the microwave. I'd suggest getting the plastic ready to cook and then do so in half minute bursts, stirring between each burst. After the third burst I'd check the temp and stop cooking at maybe 330-335 degrees. The plastic will continue to heat and could go past the 350 degrees recommended for full conversion but with stabilizer in it at the amount I noted you should be good. If you are needing to re-heat that cup of plastic, stir in a few drops of stabilizer BEFORE the plastic sets up, then re-heat.