IIRC the experiment tricked them by colouring the whites red and vice versa. So even if you could tell the difference you might not be so confident that you would know a trick was being played on you.
Give people green lollipops and a substantial percentage will describe the flavor as "lime", even if it's actually cherry.
Give people red lollipops and a substantial percentage will describe the flavor as "cherry", even if it's actually lime.
But that doesn't mean that lime and cherry actually taste the same.