It is not just the fields, but also the regions and the specific employers that can vary considerably in whether they may care about tattoos. Until you get into the workforce where you have a better idea of what field and region you will be working in, and whether various employers there care about tattoos, it is best not to get tattoos that are visible when wearing normal clothing that you would wear to work.
A forearm tattoo would mean that you may need to wear long sleeved shirts all the time if working at a tattoo-unfriendly place. Maybe that is what you prefer to wear anyway, or may be necessary anyway at some places with restrictive dress codes (e.g. suit-and-tie), but you do not know now whether that will be true several years from now (since it looks like you are either in high school or beginning of college).