What is the difference between a white and yellow icon?

When I plug in 2 different USBs, 2 different icons show up, a white one and a yellow one. I'm trying to clear the USB that has a yellow icon show up (it has more space) so I can put a movie onto it. I already have over 1000 pictures on the USB and cannot delete them, however, I can delete pictures off the USB that has a whet icon show up. I've tried multiple things and am starting to give up...😢 please help! 🙂