Red - Pink
If all you see is red, ruby is probably your first choice. It is available in a range of hues, from purplish and bluish red to orange-red. Pure reds with no overtones of brown or blue are most valuable. Rubies can be priced from $1,000-$10,000 a carat for sizes under 1 carat.

Spinel, on the other hand, is a great ruby alternative. For centuries, spinel was confused with ruby until technology was able to differentiate the two. Although rarer than ruby, fine spinel is more affordable because it is not well known. Spinel ranges in color from red to pastel shades of pink. Prices can range from $200-$2,800 a carat for sizes under 3 carats.

You might also consider rubellite tourmaline, which comes in colors from pink to red, sometimes with a violet overtone. Rubellites with a rich ruby color are most prized. Gems under 5 carats can range in price from $50-$650 a carat.

Garnet also offers a number of red alternatives. Rhodolite garnet comes in shades from pink to purplish red; almandine garnet is found in violet to pure red; pyrope is produced in yellowish red to dark red; and spessartine garnet is found in brownish orange to brownish red. Garnets can range from $10 to several hundred dollars per carat for gems under 5 carats.

Sapphire is also found in fancy pink shades and priced from $600-$4,500 a carat for gems under 2 carats. Other pink gems that are more affordable are beryls, from the same gem family as emerald: Kunzite is pinkish-violet and morganite is peachy-pink. Prices range from $75-$200 for sizes under 5 carats.

Orange - Yellow
If the color of gold is what you are after, there are many gems that have the Midas Touch. The most expensive of the orange alternatives is padparadscha sapphire. This is a very rare gem that has a strong orangey-pink color and can cost thousands of dollars per carat for small-sized stones. Fancy color sapphire also comes in yellow tones: The more clear and vivid the color, the more valuable. Prices can range from $125-$850 per carat for sizes under 5 carats.

You might also consider topaz, which is available in an array of autumn colors including yellow, gold, orange and peach. Yellow to gold topaz with no pink or red overtones can be priced from about $75 to $400 a carat for sizes under 5 carats. Imperial topaz, which is gold with pinkish-red overtones, can range in price from $100-$800 a carat for sizes under 3 carats.

Citrine also comes in shades of yellow to orange to brown at $10-$50 a carat for sizes under 5 carats. Sunstone is produced in rich orangey-red and yellow shades for $25 to several hundred dollars per cart for 1-carat gems.

Fire opal is sought after as well for its vibrant orange to orange-red hues: Priced from $50 to several hundred dollars a carat for sizes under 5 carats. Garnets also come in orange and yellow shades for reasonable prices. Beryl comes in rich yellow and golden shades, too, priced affordably from $50-$125 a carat for sizes under 5 carats.

Green
If you're green with envy for a fabulous gem, there's a variety you can choose from in this color group. Emerald is one of the most revered gems and has long been regarded as the quintessential green in nature. Gems under 1 carat can be priced anywhere from $1,000-$10,000 a carat, depending on quality.

If emerald is out of your price range, try tourmaline. Chrome tourmaline, for example, offers rich green colors and is priced anywhere from $150-$1,400 a carat for sizes under 3 carats. Fancy sapphire also comes in green (at about $50-$200 a carat for sizes under 3 carats), as well as tanzanite (at about $200-$1,000 a carat for sizes under 3 carats).

Peridot is probably one of the most popular affordable green gems on the market today. It ranges in color from yellowish-green to olive green and is priced at $30-$175 a carat for sizes under 5 carats.

Garnet also comes in green: The most valuable of the species are tsavorite (green grossular) and demantoid (green andradite). Tsavorite in a lively, strong, bright green color can command several hundreds of dollars per cart. Demantoid, considered the queen of garnet, has exceptional brilliance and a lustrous emerald-green color for several thousands of dollars per carat.

Blue - Violet
If you're feeling blue, don't fret! There's an array of gems available to cheer you up. Sapphire, of course, is considered the ultimate blue gemstone priced from $250-$3,000 a carat for sizes under 1 carat.

Spinel is a good alternative. It comes in pastel blue, gray blue, green-blue and deep blue and is priced from about $50-$1,000 a carat for sizes under 3 carats. You might also consider aquamarine, another member of the beryl family, which can be found in a range of shades from the palest pastel to greenish-blue to deep aqua. Color can be intense in larger gems; smaller ones are often less vivid. Prices range from $50-$850 a carat for gems under 5 carats.

Topaz is enhanced to create a pale to medium blue, which is rarely found in nature. It is very affordable at $5-$35 a carat for sizes under 5 carats. Tanzanite is also enhanced to a vivid blue with purple overtones. It comes in various shades of purple as well. Smaller sizes tend toward lighter lavender tones. Larger sizes typically display deeper, richer colors. Prices can range from $250-$700 a carat for sizes under 2 carats.

A sleeping giant in this color range is iolite. Found in violet blue to gray blue, iolite is gaining widespread popularity as a sapphire and tanzanite alternative: Priced affordably from $25-$125 a carat for sizes under 5 carats.

Of course, the most popular and affordable purple gem on the market today is amethyst. Sister to citrine (a member of the quartz family), amethyst comes in a variety of shades from pale lilac to violet to pale red-violet. Deep colors, particularly a rich purple with rose flashes, are the most valued. Amethyst is priced from $10-$75 a carat for sizes under 5 carats.