I found
some more information regarding the color code for the platinum color. What stood out was from an Apple's information document:
"Apple does not normally use PMS color charts or Pantone color numbers to designate the platinum color that is now the company standard. Our platinum color number on a coded PMS chart is between 420 and 421, somewhat closer to 421. (This depends on the age of the chart and the light source used for viewing it."
While a Pantone color was decided for the beige cases, Apple never officially followed through with an exact determination as it depended on many complex factors to control. However, it was close to specific color codes.
By the way, this is a good article about
the colors of Apple.