"The boy has a yellow apple."
Translation:Pojken har ett gult äpple.
If I'm not mistaken, 'gult' just shows the color. the form of gul/gult is used to reflect the type of noun you are describing. (a 'en' word vs a 'ett' word.) You still need 'en' or 'ett' in front to show that it is a single apple. you can't mix your participle (?) and your adjective. (en gult _ is wrong, so is ett gul _) All this from someone who is learning, just like you so take it with a grain of salt.... :D