In 1996, Californians approved Proposition 209, the accurately named California Civil Rights Initiative. By a 55 percent majority, voters amended California’s constitution to put an end to state-sponsored discrimination on the basis of race or sex. Proposition 209 required state government to get out of the business of quotas and preferences — to stop judging citizens by the color of their skin, and focus instead on the content of their character and the level of their ability.

I followed the story at the time, and was struck by the fact that the organizers of Proposition 209 were mostly political amateurs linked by a principled commitment to colorblindness. They shared the view of Thurgood Marshall, who argued, as the NAACP’s chief litigator during the fight against Jim Crow, that “classifications and distinctions based on race or color have no moral or legal validity in our society.”

The opponents of Proposition 209, on the other hand, included some of the savviest political operators in California, from then-San Francisco Mayor Willie Brown to the National Organization for Women. Foes of the ballot initiative were often vicious in their opposition. A Los Angeles city councilor compared it to Mein Kampf. A state senator denounced Prop 209’s chief sponsor, African-American businessman and University of California regent Ward Connerly, in nakedly racist terms: “He wants to be white… . He has no ethnic pride.”

But the proposed amendment was written in language so straightforward that voters could judge it for themselves: “The state shall not discriminate against, or grant preferential treatment to, any individual or group on the basis of race, sex, color, ethnicity, or national origin in the operation of public employment, public education, or public contracting.” Most Californians agreed with that principle — equal opportunity for all, quotas for none — and it was added to the state constitution.

Now some California legislators are pushing to repeal Prop 209. They have introduced legislation to restore racial and ethnic preferences to college admissions, government hiring, and public contracting.

The repeal bill, Assembly Constitutional Amendment 5 (ACA-5), contains a lengthy preamble that paints a doleful portrait of life under Proposition 209, especially on campus. The ban on racial preferences, it says, “reduces the graduation rates of students of color” and has had “a devastating impact on minority equal opportunity and access to California’s publicly funded institutions of higher education.” Because universities had to stop recruiting by race, claims ACA-5, “diversity within public educational institutions has been stymied.”

But Gail Heriot, a University of San Diego law professor and a member of the US Commission on Civil Rights, counters that Prop 209 “has been good for Californians — of all races,” and that ACA-5’s proponents are misstating the data. By eliminating racial preferences, Heriot wrote last week, the 1996 amendment did away with the pressure to admit minority students to competitive institutions their credentials hadn’t prepared them for. As a result, the number of underrepresented minority students at Berkeley, the most demanding University of California campus, decreased. “But those students didn’t just disappear,” Heriot observed. “Most were accepted at other campuses of the prestigious UC system, based on their own academic records rather than their skin color. On several UC campuses, their numbers increased. More important, their performance improved dramatically.”

The University of California at San Diego illustrates the effect.

In the year before Proposition 209 was adopted, only one black freshman at UC-San Diego was an honor student. But 20 percent of black freshmen became honor students the following year, noted Heriot, while the number of under-represented minority students in academic jeopardy fell dramatically.

Improved academic performance has been accompanied by steady improvement in enrollment and graduation rates, as Wenyuan Wu of the Asian American Coalition for Education recently documented in the Orange County Register:

“In the University of California system, four-year graduation rates of underrepresented racial minorities rose from 31.3 percent [before Proposition 209] … to 43.3 percent during 2001-03. In 2014, underrepresented racial minorities’ four-year graduation rate rose to a record high of 55.1 percent.”

And what is true of graduation rates is equally true of enrollment. Both in absolute numbers and as a percentage of all admissions, there are more minority students on University of California campuses than ever before. The charge that Proposition 209 “stymied” diversity in California’s public higher-education system, Wu says flatly, “is simply untrue.”

Last summer, the University of California system admitted the largest and most diverse class of freshmen in its history — without resorting to racial quotas. Fully 40 percent of the new undergraduates, reported the Los Angeles Times, were African-American, Hispanic, or American Indian.

The enemies of Proposition 209 have tried several times to get it overturned through litigation, but the California Supreme Court has twice upheld the constitutional ban on racial preferences. In 2012, the Ninth Circuit US Court of Appeals upheld the amendment as well.

California paved the way for the adoption of similar colorblind mandates in Michigan, Nebraska, Washington, Idaho, and Arizona. Truly, Proposition 209 was a landmark: In the nation’s most multiracial, multiethnic state, voters 24 years ago directed their government to stop preferring some citizens over others because of their physical characteristics. ACA-5 would undo a noble achievement. Don’t let that happen, California.

(Jeff Jacoby is a columnist for The Boston Globe).