or our guided tour around the color universe, the color wheel looks like the best vehicle ever invented.  Graphics programs have other color systems available as well (e.g.  RGB or CMYK), but these are mostly for technical purposes, while creative work is, for the most part, best done in HSV.  And of all HSV color selection panels I've seen, the one from Fractal Design's Painter (Fig. 1) is my favorite.  Of course you may use HSV color panels in other programs (many of them will show you a color bar instead of a wheel).

Fig. 1  Painter's color wheel device

The wheel slider selects the hue component, and the triangle inside (in other programs, it is a rectangle more often than a triangle) visualizes the two other dimensions for the chosen hue: its value, or brightness (vertically), and saturation (horizontally). The only thing missing for meaningful color investigation is a big enough plane to pour your color onto.  That's important because color perception varies wildly depending on the area occupied by color, so you just can't judge a color from a tiny swatch, especially if it's surrounded by other colors.  Create an empty document window (or draw a big empty rectangle) and arm yourself with a sort of paint bucket to dash your colors onto the canvas.

The first thing that comes to mind when viewing the color wheel is that it's not homogenous.  Although colors changing across the rainbow are the visible effect of monotonously increasing light wavelength, the color wheel continuum is all but monotonous.  Some colors are definitely perceived as independent and standalone (red, green, blue), others need more elaboration to localize (cyan, magenta, yellow), and all the rest are clearly perceived as mixtures or transitions of neighboring colors.  That's how our eye is designed, and inventors of color representation systems (RGB, CMYK) took this into account. The first step towards professionalism in color, as in any other craft, always leads away from the obvious---not for the sake of originality only, but being driven by interest.  I'll bet that after you've spent some time delving in the obscure corners of the color world, you won't be tempted any more by the specimens like #0000FF (pure blue) or #FFFF00 (pure yellow).  Of course sometimes you may need exactly these bright colors, but the problem with them is that they are too common and therefore carry very little information to the eye.  These are color cliches, and you can't make a good design out of cliches. So let's start from the blue at the bottom of the color wheel, moving counterclockwise and paying special attention to the intermediate and non-obvious shades.  Our point of departure is in the middle of the cold color half-circle that includes blue, green, and that light color between them that is called many names: cyan, aqua, sometimes sky-blue.  Cold colors (especially blue) are said to be psychologically tranquilizing, setting a reserved mood, and making things to appear distant and in "off-state" (a simple example is provided by D. Siegel).

The blue-aqua zone is thus a peaceful country of beautiful non-intrusive tones.  A very low-saturated, middle-light color between blue and aqua is perfect for imitating metallic surfaces (Fig. 2; click on the swatch to view the color full-screen).  The aqua itself, being a mix of equal amounts of blue and green, looks very engaging when darkened; it gives a color that's difficult to label "blue" or "green" but that combines the best features of both (Fig. 3).

Fig. 2  #80889F: Metallic Gray

Fig. 3  #006666: The Ultimate Untitled Cold Color

This observation suggests a useful rule of thumb for spotting the least used colors.  The language we use follows our habits and preferences, and if you have difficulty naming a color (other than by saying "Well, I guess that's a dark greenish blue, or bluish green, with some gray tint maybe") then it is a sure sign that the color is, at the very least, not ubiquitous.  Computer artists are relieved from the the obligation to know all those fancy color names absolutely necessary for conventional artists who are used to working with various material paints and pigments (and who lack the handy #RRGGBB notation for color references).

As we cross the green band on the wheel and start approaching the yellow, the proximity of the warm semi-circle makes wild life spring and flourish.  Dark and saturated greens, maybe a bit on the yellow side (Fig. 4) express the thrill of deep, intense, earnest color without the least sign of pallor or dimness.  As yellow overcomes, however, the green becomes swampy, muddy, saprogenic; that's the khaki color of rangers' camouflage (Fig. 5).  The subliminal implications of this "too natural" color zone are not always agreeable, so be careful.

Fig. 4  #156208: Sincerely Green

Fig. 5  #6C6C12: Color for the Military

Having passed the fiery yellow sun shining above the color wheel landscape, we enter the realm of red and brown tones.  The brown hues are no less natural than the yellowish and greenish ones, but they suggest more cultivated objects such as paper, wood, brick, or human skin. Unless you're in the midst of the red, the stimulating effect is diminished and what you get is just a warm, hearty, protected feeling (Fig. 6).  Light brown tones are reminiscent of age, ancient relics, old books.  For darker shades, you'll need to move far enough from the yellow to prevent the green tincture from appearing.

The pure red color has a very strong and obvious effect of alert, excitement, and galvanizing agitation: a "red light."  It can be used to call attention, to prompt an action, or to mark the most important element of your design.  Of course, the impact can be much aggravated by the red being the only bright and pure color of your composition. Now we're approaching the magenta zone where the warm red starts to freeze down.  Many people are fond of purple, violet, magenta tones; but to my taste, this color zone is the only one where the mix of two neighboring colors is too obvious.  Unless you've seen the color wheel, you're not very likely to guess that yellow sits between, and is thus a mix of, red and green.  However, even kids are aware that purple is a blend of red and blue.

Fig. 6  #B49A80: The Homely Warm Color

Probably the reason is that physically, here lies the seam where the linear spectrum twisted to form a wheel is welded.  The opposite ends of the spectrum, being quite different colors, are not straightforward to marry, so this part of the wheel is determined to be somehow special: the transition from warm to cold is much more sensed here than in the green-yellow area, and this may very well be the source of the appeal that purple hues have for many people.  Not that these colors are unnatural (after all, many of them are named after flowers), but they surely convey certain feeling of artificiality. (Some claim that passion towards violet reveals "mystic inclinations." Hmm.) We have finished the tour around the color wheel, but there are two very important colors that weren't mentioned.  Black and white stand out of the color spectrum, similarly to the way that zero and one stand out of the numbers continuum.  On the wheel, black and white (as well as intermediate gray tones) are both nowhere and everywhere: no matter where you're on the wheel, the lower left corner of the inside triangle (see Fig. 1) represents pure black, and the upper left corner is pure white. The black-gray-white axis is immensely important for designers because these are the only "colors without colors"; they allow us to differentiate things without assigning "colored" colors to them.  It is always an instructive exercise to check how your design looks in gray scale (e.g.  by using the "desaturate" function of Photoshop).  A composition with carefully selected colors shouldn't suffer much from this transformation. Swimming in the three-dimensional color ocean is incredibly enthralling.  Whenever you hit an interesting color, meditate on it for some time.  Try to move sliders a bit attempting to better express what you like about this color.  See how it combines with other colors.  Finally, write down the HSV or RGB coordinates for the color along with some comments on how you perceive it (your feelings may change over time in a surprising way!) and what you think it might be used for.