Under some circumstances, stars can twinkle with different
colors.12 There is no physically plausible explanation for
a multi-colored screen in the atmosphere, and even though
the refractive index of the atmosphere is somewhat wavelength
dependent, this effect, roughly a 2% effect across the
visible band,13 is too weak to cause the lens-like structures to
directly produce a visible color effect.14 For much the same
reason, the shadow pattern at the bottom of a swimming
pool on a sunny day shows no apparent color. However, a
related, indirect consequence of dispersion can explain this
phenomenon