The Character's Are look alike and They Have The Same Character Designer.
Both Have Mecha/Romance, And In Gin-iro no Olynssis the Earth is Being Invaded by a Different kind of Creature's, in Gundam Seed The Earth is Being Attacked by Coordinators.
The setting is almost exactly the same, and the plots are somewhat similar. The characters have some major differences, though. Gundam's characters were more likable, and the characters were more believable.
both have the same problems/story when it comes to the love/ relationship portion of the show. the main character (female) are both mysterious and powerful and fall in love with an average guy. both the males have childhood friends that are in love with them.
Both Anime Has the Same Type Of Story But Different Ending, In Gin-Iro No Olynsis The Earth is Being Attacked by Gardeners(Creatures From the Moon) That Trying to Erase the Remaining Human Kind and in Dragonaut the Earth is Being Attacked by the Thanatos(Giant Dragon) That Roam Around the Universe Destroying planets that contains its Dragon Egg's.
In Gin-Iro No Olynsis The Girl Main Character can Transform into a Robot and Can be Piloted Only by the Chosen One. In Dragonaut The Girl Can also Transform into a Dragon and Can be also Piloted by there Resonance.