I just into Ultraman and Ultraman Geed is my first, so far I love it. I want to ask what is the different between red ultra and blue ultra?
From what I can tell, Blue Ultras are a minority in the Land of Light. We see them in crowd shots and in the background when we see shots of their homeworld but they are clearly outnumbered by the red Ultras.
The fact is (aside from Cosmos and Agul who are from alternate universes) we almost never see a Blue Ultra leave the Land of Light with the exception of Ultraman Hikari.
Hikari was a member of the Space Science Technology Bureau as opposed to being one of the peacekeepers of the Space Garrison (who appear to all be Red Ultras). This is a role he has apparently returned to as of Ultraman Geed since it was he who invented the Ultra Capsules in the first place. This has lead me to speculate that the Blue Ultras are more suited to scientific pursuits than the rough and tumble life of a Warrior. Of course, most inhabitants of the Land of Light don’t seem to be Warriors either as we see the regular inhabitants flee from things like the attack by Belial.
One thing I will note is that the two races of Ultras do produce offspring together. We see this in a background shot from one of the movies.
My guess is that this is how Ultraman Zero was born given that he is a mix of red and blue with Ultraseven being his Father and some (as yet unseen and unnamed) Blue Ultra being his Mother.
So, most of what I can gather about the differences between Blue and Red Ultras (other than color) is speculation on my part based on evidence seen on the shows. There may be additional information I have yet to read from Japanese sources so take this response with a grain of salt.
Thanks for the Question!