And they don't get free ice cream sandwiches when the ice cream truck pulls up. Is that racism or is it economics?
Scanning books is a manual process that is much like sewing or factory work in the repetitiveness. (Maybe less skilled than sewing).
The "racism" of the situation happened years before anyone walked onto the Google campus. The socio-economic opportunities of things like safety, education, nutrition, books, time, parental involvement all feeds in to the situation where the workers in building 3.14 get one level of education and the engineers get another.
If it were true that they were segregating "people of color" then it absolutely would be outrageous. However, it is absolutely NOT true that they are segregating for reasons of color.
It's a red-herring argument.
What if the 4 to 2:30 schedule is to control traffic flow. Setting a non trivial number of workers to arrive and leave at a certain time means that the twice daily 'mega traffic jam' arriving and leaving doesn't happen.
Which puts everyone at their desks longer. Which saves money.
What if the reason that yellow badged workers aren't allowed to freely wander the rest of the google campus is down to security? Would you want low paid wage workers wandering around amongst your industrial secrets?