In the list the percentage changes are determined by the change of percentage in the past 24 hrs . The green % shows that there was a gain in the price whereas the red % shows that the price was dropped in so much %. The % might change as the 24hr period keeps changing. You can see the volume of trades in the chart that the exchange provides. You can see the volume of trade in different timings such as hourly, daily, weekly, monthly etc...
I have always thought so too, but when we now look at Tron 16 Dec 14:40h value (EUR) 0.02526683 and 24 hours later 17 Dec 14:40h value 0.03068899, a clear increase, while Worldcoinindex in red indicates a decrease of 0, 93%!