I covered that in a follow-up comment. SCOTUS unanimously held in 1959's Lassiter v. Northampton County (5 years after Brown v Board) that North Carolina's requirement that all voters be able to write out a section of the North Carolina Constitution was Constitutional, since it was applied equally to both races without a grandfather clause and no evidence of discriminatory intent.

Literacy tests are illegal and are banned under the Voting Rights Act of 1965.

Let's be a bit more specific here, why don't we? :)

SCOTUS ruled, in that case, that literacy tests were illegal if they were intended to discriminate.

The specific North Carolina Law, as you yourself noted, only required that voters be able to copy part of the North Carolina Constitution.

This was unlike many other literacy tests, some of which could be intentionally confusing and had grandfather clauses, as you yourself noticed.

As a result, on the face of it, SCOTUS ruled that this particular iteration wasn't necessarily discriminatory, and thus not unconstitutional.

However...

In practice, such tests were often administered by white voting officials in a discriminatory manner to disfranchise minorities.

Thus, Congress banned the usage of such tests by passing the Voting Rights Act of 1965.

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Scalia also apparently suggested in 2009's Ricci v. DeStefano that the "disparate impact" theory/analysis might be unconstitutional because it requires that employers (in that case) impose disparate treatment against those they believe have benefited from a disparate impact, which is the true unconstitutional act. So the guy we are commonly told also "rule[d] based on precedence and the law, not on feelings" as the parent commenter essentially suggested most discrimination is legal as long as you are careful in disguising it.

A single now-dead Justice suggesting that 'disparate impact' theory 'might' be unconstitutional means nothing.