I'm as excited as you are for this series, although I must admit I'm kind of scared they are going to screw this up since the book is simply great (definitely the greatest medieval fantasy book ever)... the thing about the Lannister's hair color is a detail but it's weird, why didn't they keep the blonde color? And as you said it's more than a detail in the book, so it's a strange choice.
Anyway, the trailer reassured me a little bit, I just hope it stays true to the book and, most importantly, that it is well played by the actors (I didn't envision Tyrion like the one we see in the trailer at all ).
I have faith, it's Peter Dinklage, he's one of the best character actors around, never mind the best little person actor
EDIT: another nit pick, and mabey it's just the color in the trailer, but Danni's hair doesn't look very silver.
Mabey it's that they don't want to shock the audience with an unnatural hair color, but I've always pictured her like she is in the card game art, with noticeably silver (not grey) hair.
That will be another interesting transition. In the trailer here she looks sufficiently innocent for the first book, but I hope that actress can pull off the character development.
Danni's transition from "scared little girl" to "daenerys stormborn, mother of dragons" and general butt whooping character.