Holding Shift (or Ctrl) to move RGB sliders together in Color panel doesn’t work when color is white
A Help article on Color panel states we can hold Shift (also works for Ctrl, although unspecified there) to move color channels’ sliders 'in tandem', together, — http://helpx.adobe.com/illustrator/using/default-keyboard-shortcuts.html#keys_for_the_color_panel
This indeed works, in both RGB and CMYK modes (not in HSB, since its values won’t benefit from it).
However, if all three RGB sliders are at 255/100% (white), this mode doesn’t work — please see the GIF attached.
It probably makes sense for CMYK, where it’s not clear if 0-0-0-0 should become something like 24-24-24-24, but it totally makes sense for RGB, where we expect to get a gray color.
Thanks to Franck Payen for bringing attention to this old problem. It’s not as irritating as others, but still it should be fixed.

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Kris Hunt commented
One thing that's bothered me for a long time is that, when you're in the RGB color space, it is impossible to move all three RGB color sliders to the left equally to get a light gray. Meanwhile, it IS possible to move all three sliders to the right equally from black by holding down the Shift key while dragging the sliders. Please fix it so holding down Shift will allow you to drag all three sliders simultaneously from white.
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Affinity Designer does it worse, BTW.
If any slider is at 255, holding Shift won’t work.
And it won’t work for clear black, unlike in Illustrator, — at least one slider ahve to be non-zero.