It is by no means a merely arbitrary rule.  Colours are actually warm or cold in temperature, as well as in effect upon the eye or the imagination, in fact the words cover a long-tested fact.  I remember being told by a painter of his placing a red sunset landscape upon the flat roof of a studio building to dry, and on going to it a few hours afterward he found the surface of it so warm to the touch—­so sensibly warmer than the gray and blue and green pictures around it—­that he brought a thermometer to test it, and found it had acquired and retained heat.  It was actually warmer by degrees than the gray and blue pictures in the same sun exposure.

We instinctively wear warm colours in winter and dispense with them in summer, and this simple fact may explain the art which allots what we call warm colour to rooms without sun.  When we say warm colours, we mean yellows, reds with all their gradations, gold or sun browns, and dark browns and black.  When we say cool colours—­whites, blues, grays, and cold greens—­for greens may be warm or cold, according to their composition or intensity.  A water-green is a cold colour, so is a pure emerald green, so also a blue-green; while an olive, or a gold-green comes into the category of warm colours.  This is because it is a composite colour made of a union of warm and cold colours; the brown and yellow in its composition being in excess of the blue; as pink also, which is a mixture of red and white; and lavender, which is a mixture of red, white, and blue, stand as intermediate between two extremes.

Having duly considered the effect of light upon colour, we may fearlessly choose tints for every room according to personal preferences or tastes.  If we like one warm colour better than another, there is no reason why that one should not predominate in every room in the house which has a shadow exposure.  If we like a cold colour it should be used in many of the sunny rooms.

I believe we do not give enough importance to this matter of personal liking in tints.  We select our friends from sympathy.  As a rule, we do not philosophise much about it, although we may recognise certain principles in our liking; it is those to whom our hearts naturally open that we invite in and have joy in their companionship, and we might surely follow our likings in the matter of colour, as well as in friendship, and thereby add much to our happiness.  Curiously enough we often speak of the colour of a mind—­and I once knew a child who persisted in calling people by the names of colours; not the colour of their clothes, but some mind-tint which he felt.  “The blue lady” was his especial favourite, and I have no doubt the presence or absence of that particular colour made a difference in his content all the days of his life.

The colour one likes is better for tranquillity and enjoyment—­more conducive to health; and exercises an actual living influence upon moods.  For this reason, if no other, the colour of a room should never be arbitrarily prescribed or settled for the one who is to be its occupant.  It should be as much a matter of nature as the lining of a shell is to the mussel, or as the colour of the wings of a butterfly.