Drupal\color_field\Plugin\Field\FieldFormatter\ColorFieldFormatterSwatch::getShape(): Return value must be of type array|string, Drupal\Core\StringTranslation\TranslatableMarkup

If 3.x requires PHP 8.x then it should have a requirement in its composer.json file stating this.

Drupal requirements have been messed up as of late as far as PHP requirements. If you look at D9.4 status report it states 8.x is a requirement; but it is not.

I just ran into this PHP 7 incompatibility. What can be done to address this?

I also just ran into this PHP 7 incompatibility. This requirement should definitely be in the composer.json file.

"Make it clear" means to me: in composer.json :-)

Regards,

Setting back to fixed.
At time of release PHP 7.4 was past end of life.
definitely would have been better to include that in the dependencies but should be moot point by now.