Shortly after reaching the International Space Station, the trio spoke to callers on the phone, including with family members who wished them a successful mission. When asked by a caller about their clothing choice, Artemyev responded that each crew is allowed to pick its own colors from a stock supply of equipment.

“We actually had a lot of yellow material, so we had to use it,” Artemyev explained. “So that’s why we had to wear yellow.”

Russia’s space force also denied that the color was meant to reflect the Ukrainian flag. It said the uniform’s design reflected the colors of Bauman Moscow State Technical University, where the cosmonauts studied.

The three Russians’ sartorial decision triggered discussions on social media about whether it was a deliberate reference to the war in Ukraine, where Russian forces have unleashed torrents of artillery fire, missiles and bombs over the past three weeks. Russian President Vladimir Putin has controversially tried to justify the offensive by claiming that it was launched to “de-Nazify” Ukraine.

Former NASA astronaut Scott Kelly, who commanded three expeditions aboard the International Space Station, tweeted Friday, in both Russian and English, that the three Russian cosmonauts arrived in “Ukrainian yellow!” Fellow astronaut Terry Virts was similarly enthused, tweeting, “Wow. Just wow. Well done.”

Space enthusiasts and observers were particularly keen on knowing whether the suits are meant as support for Ukraine, because Russian authorities have cracked down on antiwar sentiment since late February. The Kremlin has shut down independent media outlets, banned some social media platforms and punished activists who dare to speak out.

This has left little space for people in Russia to access stories of the mounting humanitarian crisis in neighboring Ukraine. Those who support Putin’s invasion have also launched their own pro-war campaigns, including using the letter “Z” to signal their approval.

The trip to the International Space Station comes as escalating tensions between the United States and Russia strain the countries’ space partnership. Dmitry Rogozin, the head of Roscosmos, threatened earlier this month to cut off the supply of Russian-made rocket engines used on rockets that fly supplies to the space station. But NASA leadership has dismissed the idea that the collaboration is fraying.

Marisa Iati contributed to this report.