Lucretius, De Rerum Natura
William Ellery Leonard, Ed.

     Besides, since colours cannot be, sans light,
And the primordials come not forth to light,
'Tis thine to know they are not clothed with colour-
Truly, what kind of colour could there be
In the viewless dark? Nay, in the light itself
A colour changes, gleaming variedly,
When smote by vertical or slanting ray.
Thus in the sunlight shows the down of doves
That circles, garlanding, the nape and throat:
Now it is ruddy with a bright gold-bronze,
Now, by a strange sensation it becomes
Green-emerald blended with the coral-red.
The peacock's tail, filled with the copious light,
Changes its colours likewise, when it turns.
Wherefore, since by some blow of light begot,
Without such blow these colours can't become.
     And since the pupil of the eye receives
Within itself one kind of blow, when said
To feel a white hue, then another kind,
When feeling a black or any other hue,
And since it matters nothing with what hue
The things thou touchest be perchance endowed,
But rather with what sort of shape equipped,
'Tis thine to know the atoms need not colour,
But render forth sensations, as of touch,
That vary with their varied forms.