Martin Luther King Jr. Day happens a week from today, on Monday Jan. 19. But it's not a holiday for the loyal employees of Apple. They have to go to work.

MLK Day is a federal holiday, meaning government offices are closed. Companies don't have to observe the holiday, but many do, if only because it seems like the right thing to do. In Silicon Valley, where companies have been taking heat for their incredible lack of diversity, observing the MLK Day holiday seems like a smart move if only for the sake of "optics," as they say.

Facebook, Google, Twitter and Yahoo all give employees the day off.

But amazingly enough, Apple does not. Apple! This seems incredible. After all, is there any company in the world that makes as much effort to cultivate and present an image of being left-leaning and progressive as Apple does?

Before going any further, I must cop to something: Gawker Media, which owns this blog, also does not make MLK Day a paid holiday for its employees. This sucks.

On the other hand, Gawker never used Martin Luther King Jr.'s image in its advertising.

But Apple did. Check out this old "Think Different" campaign, where King appears alongside other legendary Apple salesmen like Einstein, Gandhi, Muhammad Ali and Picasso:

It's weird that Apple does not observe this holiday, especially since I've been told that Apple CEO Tim Cook keeps a photograph of MLK in his office and considers MLK one of his personal heroes.

Not long ago, Cook talked about his own experience growing up in Alabama in the 1960s, seeing and experiencing discrimination, and even witnessing a cross-burning. Watch this speech, which is genuinely moving:

I believe Tim Cook is sincerely committed to diversity. Apple's top management team isn't exactly the most diverse group of people you've ever seen, but it is better now, under Cook, than it was under Steve Jobs.

In the Jobs era, the Apple management team had zero people of color. Now there are two. That is Cook's doing.

So why not observe MLK Day? After all the news that came out last year about the dismal diversity statistics in the Valley, not observing the holiday looks pretty tone-deaf. And it is not often that Apple is accused of being tone deaf. If there is one thing Apple has always been good at, it's marketing and PR and image management.

To be fair: Apple also does not give employees paid holidays on Presidents' Day or Columbus Day. And Apple does mark the King holiday in its own way, with a program in which the company donates $50 to a charity whenever an employees does an hour of volunteer work. Ordinarily Apple donates $25 for each hour worked, but in honor of MLK the company is doubling the rate from Jan. 19 to the end of March.

Nevertheless, that's not the same as just observing the holiday. Then again, does that really matter? Is the holiday itself a big deal? I asked Rev. Al Sharpton. He seems to think so.

"This is a national American holiday, and Apple is a symbol of the American technology industry. What signal are you sending?" Sharpton says. "Are you indicating that this holiday is less than important? For all the talk about the technology industry trying to become more diverse, this makes it harder for us to believe that this is credible."

Sharpton's other point: "So many diverse people are consumers of Apple products. What are you saying to them? If this were some old Wall Street company, we'd be outraged. We wouldn't be making excuses for them. Does Apple get a free pass because they're a part of the new tech America? Are we saying that in the new tech America, Dr. King doesn't matter?"

Vivek Wadhwa, a Stanford Fellow and advocate for greater diversity in Silicon Valley, says he's not surprised to see Apple not marking the holiday.

"Apple has always been a worst offender when it comes to diversity," he says. "Look at its board and management team. For all the good things we say about Apple's innovation, it really hasn't been exemplary in improving itself. Apple and the industry need to get with the times."

A lot of companies in Silicon Valley do observe the holiday, including Andreessen Horowitz, Ebay, Glassdoor, HP, LinkedIn, Square, and Uber, plus the four I mentioned up top.

Microsoft has two "floating holidays" and a lot people use one of them for MLK Day, a spokesman says.

Tech companies that don't observe the holiday include Adobe, IBM, Qualcomm, Sequoia Capital — and Intel, whose CEO, Brian Krzanich, just last week made a big speech about diversity at CES in Las Vegas, with Jesse Jackson sitting in the front row. Krzanich committed to spend $300 million to increase the diversity of its workforce by 2020.

Will Apple change its ways? I'm betting that Cook will reverse Apple's policy on MLK Day, and that by this time next year Apple employees will be getting ready for a three-day weekend.