On Sense And The Sensible   

that the Pythagoreans named the superficies of a body its 'hue', for

'hue', indeed, lies at the limit of the body; but the limit of the

body; is not a real thing; rather we must suppose that the same

natural substance which, externally, is the vehicle of colour exists

[as such a possible vehicle] also in the interior of the body.

Air and water, too [i.e. as well as determinately bounded bodies]

are seen to possess colour; for their brightness is of the nature of

colour. But the colour which air or sea presents, since the body in

which it resides is not determinately bounded, is not the same when

one approaches and views it close by as it is when one regards it from

a distance; whereas in determinate bodies the colour presented is

definitely fixed, unless, indeed, when the atmospheric environment

causes it to change. Hence it is clear that that in them which is

susceptible of colour is in both cases the same. It is therefore the

Translucent, according to the degree to which it subsists in bodies

(and it does so in all more or less), that causes them to partake of

colour. But since the colour is at the extremity of the body, it

must be at the extremity of the Translucent in the body. Whence it

follows that we may define colour as the limit of the Translucent in

determinately bounded body. For whether we consider the special

class of bodies called translucent, as water and such others, or

determinate bodies, which appear to possess a fixed colour of their

own, it is at the exterior bounding surface that all alike exhibit

their colour.

Now, that which when present in air produces light may be present

also in the Translucent which pervades determinate bodies; or again,

it may not be present, but there may be a privation of it.

Accordingly, as in the case of air the one condition is light, the

other darkness, in the same way the colours White and Black are

generated in determinate bodies.

We must now treat of the other colours, reviewing the several

hypotheses invented to explain their genesis.