PERHAPS ash you read your Weather Eye this morning you are in the very act of pouring milk over the colonically friendly sunshine breakfast of your choice. But pause a whit, and ask yourself why the liquid that you pour is white. It consists of tiny globules of fat suspended in a water base, and insofar as these particles have any hue at all, it is not white; the milk takes its colour from the action of sunlight on the mixture.
Light is a sequence of electromagnetic waves to which our eyes are sensitive. It acquires its colour from its wavelength: blue light has a very short wavelength, "red waves" are relatively long, and the other colours of the spectrum fall somewhere in between. The light emanating from the sun is a mixture of them all: we call it "white". As light waves try to make their way in a straight line through any medium they are "scattered", or deflected from their original path, by any very small obstructions in their way and the effectiveness of the scattering for any particular colour depends on the six of the particles concerned.
Smoke particles, for example, are of such a size that they scatter blue light very efficiently, but the red and orange wavelengths are largely unaffected. When we look at the smoke rising from a cigarette, therefore, we see - not the particles of smoke themselves - but the blue portion of the sunlight selectively scattered in our direction by the particles of the pollutant. When the cigarette smoke is inhaled and then exhaled, the moisture now condensed upon the particles has the effect of making each one bigger than it was collectively they now scatter light effectively in all the visible wavelengths, and this mixture of scattered colours makes the smoke appear as white.
But back to breakfast, and the colour of milk.
The fat particles in the milk are of such a size, like those of cigarette smoke, that they scatter the blue light more effectively than any other: this can be seen from the bluish tinge to the film of milk adhering to an emptied glass. But milk is "optically thick"; there are so very many particles per unit volume of the liquid, that sooner or later even the "red" and other waves, after multiple encounters, are scattered to emerge from the liquid towards a waiting eye. Moreover the fat globules have the quality of absorbing very little of the light, so waves of every colour survive these adventures more or less unscathed. The eye receives all the colours of the spectrum from the milk, and adds them up to the familiar colour that we know as white.