If they were asking about actual color of the dress that you cannot see, what the fuck is the point? That's like saying, we put orange cat in fully closed box. What color is the cat? And you then claim it's not orange, it's black because there is no light inside the fully closed box so the cat is actually black. That's the level of stupid argument with this stupid ass dress.
I can also shoot a white dress to look entirely blue because I'm gonna use cool white light at 9000 fucking Kelvins and fuck up the cameras white balance to make shit look anything but its actual color. I can also take a normal photo and then just drag some sliders in photo editor and fuck up colors and then ask some bullshit question about colors and then go like "well, achtually it's not that color".
It's also funny when people argue it's not actually white because color picker says it's light blue. Firstly, color motherfucking temperature. Secondly, open color wheel and see where it's positioned. It's in the white segment mildly nudging towards blue. The part where I'm not gonna argue is perception of gradients. This isn't "this gold color is actually black bullshit", but actual science where people perceive correct colors differently. For someone a certain gradient of red is perceived as lighter or darker compared to someone else. But certainly isn't perceived as green. Or black. Or whatever other basic color.