It could be merely descriptive, if you only came across it when e.g. discussing people who can get away with skipping the sun screen. When it’s the category that gets brought up in the newspaper when someone becomes CEO, instead of myriad other categories that could apply, then it’s prescriptive. It is a pattern that shapes how non-white people are perceived and gives primacy to their skin color.

Your point about “racism” illustrates how focusing on skin color leads you astray from the outset. There is no single coherent thing called “racism” that applies to all “people of color.” Indian Americans face the ordinary prejudices people of different ethnic groups have towards each other. It’s the same prejudices Indians have towards Chinese or vice versa. Jewish people almost certainly face more prejudice in America than Indian Americans. We acknowledge that prejudice, but don’t go so far as to categorize and define them based on it.

Meanwhile, the “racism” faced by ADOS and indigenous people is different in kind. The prejudice is just the tip of an iceberg, and beneath that are the realities of being a minority population that was enslaved and brought to this country by the majority population or one that was nearly wiped out by the majority population in settling the country. The point is not that “racism” knows how rich you are. The point is that “racism” that isn’t accompanied by structural socioeconomic disparities isn’t meaningfully the same thing as “racism” that is.

And it’s not useful to any minorities to conflate these categories. Thinking in terms of “people of color” is bad for black and indigenous people. Because fixing prejudice based on skin color won’t meaningfully help them. At the same time, it’s not good for Indian Americans to falsely believe they face structural disparities when they do not.