The history of dandyism is a bit of a battle between the peacocks, and the gentlemen. Is it better to be noticed for how one dresses, or to dress such that one is remarked for one's presence? "Beau" Brummel the father of dandyism was clear on that matter when he stated laconically "if John Bull turns his head to notice you when you pass, you are not well dressed. Still, is this the final word?
In the modern world with it's almost complete loss of fashion sense especially among men, it is even easier, if well dressed, to be swallowed by the quality of one's wardrobe. What's a Dandy to do? How can a man dress sharply and yet be the master of his own fashion?
Let's look at a couple of elements and how they can be used with out becoming unruly.
First of all is the question of color. Color can shock or soothe, and becomes a [if not the] key element in creating an ensemble that compliments. First of all contrasting colors are going to be a problem. The were originally used by theatrical men who wanted to grab attention and such combinations were designed to either please they eye by their extravagance, or invoke fear of thrill with their sinister appearance. Neither of these is the effect of the Dandy. So what colors to use? Well, it begins with your skin, eyes and hair type. If you are tall dark and handsome, then your can wear a little extra color, as your skin/hair contrast will compliment it, but if you are a fair skinned, fair haired man you are going to have to find a more subtle style.
Generally there are four color trends which match [at least roughly] the four seasons, and are in fact named for them.
Winter: I'll begin here as it's the first season in the calendar year [not the fiscal year, but we're talking about Dandies who generally overlook such trivialities]. Winter colors tend to be darker, and more jewel toned. black, grey, dark blue, and dark red usually make up the canon. These colors make for a gaunt look and are very dignified looking. Formal wear is almost exclusively "winter" in its flavor. Older gentlemen will generally wear a great deal of "winter" outfits as it gives them a dignified look.
Spring: With the warmer weather [or a warmer attitude] comes the spring look. This look is most known for pastels, and tweeds. Lighter colors and soft hues it gives a pleasant and youthful look to the man who wears it. Younger men [or the young at heart] can wear Spring outfits and it will give them a friendly youthful look. This look may make an older man look "juvenile" so care needs to be taken when choosing this lighter style.
Summer: The bright and light. This style is for fun and energy. Colors are whites, yellows, light reds, and light blues. This style is for fun and betrays no solemnity or real dignity. A man over 50 really cannot wear much "summer" wear, as it makes him look very eccentric.
Fall: On a somber not the "fall" style is full of darker jewel tones, and even more textured fabrics make this style fairly versatile. Rich browns, dark/brick reds, dark blues and greens are "fall" colors. This is a very popular style with many peacocks because of the rich color combinations it allows. This style really is among the most versatile as it is fairly easy to create an appealing ensemble with a mixture of dark earth tones and jewel tones.
The key is to knowing what style you like, what goes best with your personal make up, and putting together outfits that compliment you, rather than stand out in spite of you.
Another important aspect is to put together an ensemble with out too many accessories. They are like jewelry, less is more. A hat, gloves and a walking stick looked fine for a gentleman in 1808, or even 1908, but not in 2008. Unfortunately modern culture [if such a term can even be used] does not well support a well dressed gentleman. A hat is fine if it's very sunny, or very cold. Gloves can be added in the case of cold, but a walking stick should only be used to costume events and fancy parties.
Se nosce! The Latin adage is even more important in fashion than philosophy. A man who knows his style, and dresses to match his mine without too many extras can create a truly great impression, not because his outfit is great, but because he looks great in his outfit.