ParseError in color_field (2.5.0) to color_field (3.0.0) update

I encountered this, too. I'm on PHP 7.4. This is the line in question:

protected function getColorFormat(?string $format = NULL): array|MarkupInterface {

It looks like this is an issue with PHP 7 backward compatibility.

Confirmed. Marking this as a duplicate of 🐛 Drupal\color_field\Plugin\Field\FieldFormatter\ColorFieldFormatterSwatch::getShape(): Return value must be of type array|string, Drupal\Core\StringTranslation\TranslatableMarkup Needs work

thanks, I was on 7.4 as well.