Now you know

From the Times Sky Watch, Week of April 8 (4/8/07)

"... reddish Betelgeuse, orangish Aldebaran and yellowish Pollux ...
brilliant topaz Arcturus ... Even as you observe these stellar colors,
do you notice that they are only recognizable in the brightest stars?
That is because of the physiology of the eye -- more specifically,
the fact that the color sensors on the retina, the cones, are
insensitive to faint light. Under dim light the rods in the retina
take over. But their greater light sensitivity is offset by their
colorblindness. That is why we see all faint stars as white. But
if we look at them through binoculars or a telescope, their
amplified brightness stimulates the cones, which detect their
color.