Other systems I think should be showing blue dots (I've researched Col Cost -5% and they show 1. 9 on my Potential Colonies list) show dots as if those were 2-2. 9 suitability worlds.
Maybe the Galactic Map doesn't use colony cost reduction tech but looks what the planet's base colony cost is. This would explain why the 2.0 worlds (good temperature, but no suitable atmosphere) are light blue instead of dark blue. So only worlds with a CC of <2.0 before the colony cost reduction is calculated in would show dark blue.
That way someone could still see the difference between worlds, as dark blue worlds usually only need temperature adjustments.
Also I myself had a problem with the asteroids in a game. I assume that while they can't be colonized, they still show as a suitable colony dot in the galactic screen. The particular race were methane breathers living on low gravity planets. As some larger asteroids would have a suitable gravity, but asteroids aren't colonizable due to performance reasons (AFAIK), systems (nebulae) with nothing but a few asteroids would still show a few light blue dots on the galactic map.
