The problem comes up when making policy. Let's say there are green people who average 10% less intelligent than purple people, and that jobs for smart people pay better than jobs for stupid people. Waving a magic wand to end racial prejudice and provide equal schools, safety, housing, and food would still leave the average green person worse off than the average purple person. You could wave the magic wand to end racial inequality of opportunity until your arm falls off and not get rid of the average pay gap between green and purple people because less intelligent people are being paid less no matter whether they are green or purple but more of them are green. If you want the average green person to be as well off as the average purple person, you need to make jobs for stupid people pay as well as jobs for smart people or take money from the mostly-purple rich and give it to the mostly-green poor.
If you are a commoner in an absolute monarchy or a subject in a dictatorship, maybe it's best for you to forget about that because policy-making is in the hands of your betters. But you probably live in a democracy which means you have a small say in policy and need to think about whether a policy will do what you want before you support it.
Quoting your previous post:
I'm running with your "for the sake of argument" scenario and constructing a fairy-tale-level example to illustrate why the average citizen of a democracy has a reason to care. Namely, the average citizen votes on policy, and a policy of equality of opportunity doesn't lead to ethnic equality when there is a big gap in average intelligence, or tenacity, or health, or what have you.
If I've got the statistics right, on average 75 of those random green people will be less intelligent than you (and 25 more intelligent). I am surprised and expected the numbers to be less skewed. I wouldn't expect 75 of those random green people to also be poorer than you, but 60-65 sounds reasonable.
Then my post did its job of making you think about what policy you'd vote for in this situation.