In previous postings, I have explained why different aspects of a suit make it more formal. Broadly speaking, a material that is smoother, darker and plainer will be more formal. A dark navy worsted is smarter in all three ways than a mid-grey checked flannel.

This is an easy way to assess the propriety of a particular suit to an occasion. If your suits were to sit in the wardrobe in order of formality – from smart to sporty – it would be simple to pick the one that best suits that day’s activities.

What is often forgotten, however, is that the same guidelines apply to shirts.

It’s fairly obvious that a checked shirt is more casual (plainness), as is an Oxford-weave cloth (smoothness). But colour is often ignored – yet it is probably the most important of these three variables. White shirts are still more commonly worn for business in the US, because they are always and everywhere smarter than blue. In the UK, blue shirts are more accepted but then we have a tradition of sportier shirts against a background of simple ties and suits (hence Jermyn Street).

This is why coloured shirts traditionally had white collars and cuffs – nothing else would show off the very smartness of being able to keep material clean, crisp and laundered. It is also why pink, despite its reputation in the US, is more formal than blue as a shirt colour. Pink is paler (usually) than blue: a lighter and a smarter colour.

Even a yellow or cream shirt is smarter than blue (I was converted to the idea of a pale yellow shirt by the purchase of a Ralph Lauren Purple Label example in the sales last year). Essentially, the lighter the colour smarter it is.

And cream shirts bring me on to my next point. When shirts are worn casually, they need to be taken down a formality point or two. White is too smart to go well with jeans and trainers, particularly if it has other dress shirt attributes (French cuff, lack of placket on the buttons, stiff collar, cutaway collar, lack of chest pocket). A cream or khaki shirt is the first option to consider.

Let’s take an example – I often wear the jacket to a checked, woollen suit as a separate piece with jeans. The shirt to go with this ensemble needs to be casual; it cannot be white. Yet blue, to my particular taste, doesn’t suit the check of the jacket. I therefore nearly always go with a pale khaki or cream – it suits the check yet is one notch down from a formal white. It doesn’t have the high contrast of white; it doesn’t pop but recedes.

So always consider the colour of your shirt choice first. If worn casually, blue is the default but khaki, cream or even grey work very well.