Hello Sam75,
Among the US Visa Application requirements, it's mentioned that you must be a permanent resident in a country where you currently live.
Therefore with the 3 years residence permit, it will be difficult for US councilor to grant you a Visa, but it could also be possible.
As for the issue of your country passport it's much better to have your country passport than the grey passport or blue passport.
If you get your country passport you have to turn it over to the Ausländerbehörde so that they will put the passport number in your residence permit.
I hope my answers will help you until you get a response from the experts.
Kind regards