it depends where your permanent residency is. US citizen aswell can trade FX the way european do when the open a account in europe. you are free to let your local authorities know if you got that account or not, they can not check it on you. if you earn and hide the account you are doing tax fraud, if you lose noone cares. rule of thumb, USA doesnt know what youre doig in europe as long as you dont generate big profits which you then spend in USA.
my advice, go on open one and dont worry about Us regulations uless you make big enough money to have a reason to worry whe you do money you can always leaglize it with help of tax consultants etc.
usually acount openings with repuatable brokers it is required to check you on your US laws, they ask you questions on your status if you lived in USA and if you have any trading connection activities in usa, the questions are designed to find out if you are allowed to open one or not. if your broker (a reputable one) grants you account after asking all those question then its very likely you have no issues anymore with the ever boring american tax offices-.