Every major colored stone should be properly graded for the 4-C's' . . .

Color, Cut or Clarity and Carat Weight

The order of value is unfortunately never totally agreed on by those that grade a colored stone (including the Gemological Institute of America and its own trade laboratory the Gem Trade Laboratory). However, it is the opinion of Mackley & Company the order should be as presented for determining the maximum value of a colored stone.
We will proceed to give nomenclatures for the color, cut and clarity of a colored stone followed by a definition of carat weight. Any credit for the following should primarily go to the GIA and the AGL for the developing of ones' thought process in nomenclature. Imagine a grader using one set of criteria and another a completely different standard. (This actually goes on today.) This is not to say that all of the following was developed by the GIA, but it is to say the thought process for the grading of a colored stone is accepted as the standard and probably came prior to the GIA's introduction of their standard. Probably the American Gemological Laboratory (AGL) brought about most of the development of colored stone standards. Mackley & Company refers to the following as a subjective scientific or educational conjecture method.

Color Colored gemstones are graded with the use of words or a system. Words are like: A slightly light yellowish Green. A System can be either GemDialogue (Rubin), eWizard (Stuller). ColorScan (AGL-discontinued), ColorMaster (Gem Instruments division of the GIA-discontinued), and the prescribed methods of the GIA, AGL, AGA, ASA, or a combination thereof at the discretion of the gemologist. Each method should be referenced.
The AGL color nomenclature for tone is from colorless to black (0-100) and its color rating is from excellent to poor (1-10). In essence, there is no standard other than a word system. The GIA color nomenclature has just changed their system. The GemDialogue system of composed of a modifier-hue with a tone and then possibly with a colormask. The ColorScan is a hue and tone noted with a number. Examples of both systems are available in the office of Mackley & Company, Inc. Mackley & Company will utilize the word system along with GemDialogue for most situations.

Clarity Clarity is usually the second most important factor when evaluating colored stones. Clarity should be checked first with the unaided eye and then under 10X with darkfield illumination. The primary clarity systems used are the AGL and the GIA. The AGL and GIA (with the three types) systems are listed as follows:
AGL GIAType Iusuallycleanish GIAType IIusuallyincluded GIAType IIIhighlyincluded DESCRIPTION
FL VVS Minute to not detectable
LI1-2 VS VVS Minor
MI1 SI1 VS VVS NOTICEABLE to obvious
MI2 SI2 SI1 VS Noticeable to OBVIOUS
HI1 SI2 SI1 OBVIOUS to prominent
SI2 Obvious to PROMINENT
HI2 I1 I1 Prominent (moderate affect on appearance or durability)
I1 Prominent (considerable affect on appearance of durability)
EI1 I2 I2 Prominent (severe affect on appearance or durability)
I2 Prominent (severe affect on transparency or durability)
EI2 I3 I3 I3 Prominent (severe affect on beauty, transparency and durability)
EI3 Déclassé Déclassé Déclassé Stones not transparent because of inclusions.

Cut The cut can affect the color grade of a colored stone either positively or negatively and can have a greater affect on the overall grade. Designer cut colored stones can add a premium to the overall value. The GIA cut grading system is a detailed system that grades the proportions and finishes of colored stones and relates it to a final grade of 1 to 10. The following proportions and finish guidelines should be considered when evaluating the cut of colored stones.
10 9 . . . . . . . . 8 7 . . . . . 6 5 . . .4 3 . . .2 1
Excellent . . Very Good . . Good . . Fair . . Poor

PROPORTIONS - Outline balance, length to width ratio, profile balance, total depth percentage, crown height and pavilion depth, bulge, table size, brilliance, extinction and windowing.
FINISH - Polish, symmetry, and facet survey.
Some colored stones need special consideration regarding cut. Fancy cuts not normally used for colored stones may command a higher value. Shapes not normally cut due to the nature of the rough may also command higher values.

Carat Weight Simply, two tenths of a gram is a carat. Each carat is made up of 100 equal parts called points.

The other two characteristics of Buying Gemstones are Cost (everyone has a budget) and Confidence.(you are not going to purchase unless you feel good about it, are you?).