SpaceX employees used to monitor Talulah Riley's hair color to determine if Elon Musk would be in good mood

Mark Lennihan/AP; Joshua Roberts/Reuters; and Melia Robinson/Business Insider

Elon Musk and ex-wife Talulah Riley.

• Elon Musk is known for being moody at times.
• Some former employees at SpaceX told The Wall Street Journal they could tell Elon Musk's mood based on the hair color of actress Talulah Riley, when they were married.

Elon Musk has earned a reputation for his humor as well as his outbursts, which are often chronicled in a series of tweets.

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But some of his employees learned to look beyond Twitter to gauge the tech billionaire's mood.

In interviews with The Wall Street Journal, former employees at Musk's company SpaceX said they "tried to anticipate his mood by following the news of his personal life, even tracking the hair of actress Talulah Riley when she was his second wife," the Journal reports.

Senior managers told the Journal they avoided pitching new ideas or raising issues when Musk was in a bad mood.

They believed Musk was "happiest when her hair color approached platinum," according to the Journal.

After his first divorce from a Canadian novelist, Musk began dating Riley, a British actress who's best known for her role in "Westworld."

They married in 2010. Two years later, news of their divorce became public when Musk tweeted: "It was an amazing four years. I will love you forever. You will make someone very happy one day" at Riley on Twitter.

The couple remarried in 2013 and divorced again in 2016.

Read more: Inside the turbulent personal life of Elon Musk, who called his estranged father 'a terrible human being' and who says he must be in love to be happy

Musk's stormy personal life has made him a central figure of tech gossip in recent weeks. The Tesla and SpaceX CEO recently stopped following pop musician Grimes - who he's dated since at least spring - on Twitter. The two appear to have unfollowed each other on Instagram, as well. It's unclear whether the couple is still in tact.

For what it's worth, Grimes was last photographed stepping out with Musk at SpaceX event in July - as a brunette.

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