Colours in the Universe which are made by Light, and depend not
on the Power of Imagination, are either the Colours of homogeneal
Lights, or compounded of these, and that either accurately or very
nearly, according to the Rule of the foregoing Problem._

For it has been proved (in _Prop. 1. Part 2._) that the changes of
Colours made by Refractions do not arise from any new Modifications of
the Rays impress'd by those Refractions, and by the various Terminations
of Light and Shadow, as has been the constant and general Opinion of
Philosophers. It has also been proved that the several Colours of the
homogeneal Rays do constantly answer to their degrees of Refrangibility,
(_Prop._ 1. _Part_ 1. and _Prop._ 2. _Part_ 2.) and that their degrees
of Refrangibility cannot be changed by Refractions and Reflexions
(_Prop._ 2. _Part_ 1.) and by consequence that those their Colours are
likewise immutable. It has also been proved directly by refracting and
reflecting homogeneal Lights apart, that their Colours cannot be
changed, (_Prop._ 2. _Part_ 2.) It has been proved also, that when the
several sorts of Rays are mixed, and in crossing pass through the same
space, they do not act on one another so as to change each others
colorific qualities. (_Exper._ 10. _Part_ 2.) but by mixing their
Actions in the Sensorium beget a Sensation differing from what either
would do apart, that is a Sensation of a mean Colour between their
proper Colours; and particularly when by the concourse and mixtures of
all sorts of Rays, a white Colour is produced, the white is a mixture of
all the Colours which the Rays would have apart, (_Prop._ 5. _Part_ 2.)
The Rays in that mixture do not lose or alter their several colorific
qualities, but by all their various kinds of Actions mix'd in the
Sensorium, beget a Sensation of a middling Colour between all their
Colours, which is whiteness. For whiteness is a mean between all
Colours, having it self indifferently to them all, so as with equal
facility to be tinged with any of them. A red Powder mixed with a little
blue, or a blue with a little red, doth not presently lose its Colour,
but a white Powder mix'd with any Colour is presently tinged with that
Colour, and is equally capable of being tinged with any Colour whatever.
It has been shewed also, that as the Sun's Light is mix'd of all sorts
of Rays, so its whiteness is a mixture of the Colours of all sorts of
Rays; those Rays having from the beginning their