Some people call stripes of color of the grain 'figure', in which case virtually all wood has 'figure'. Some might refer to 'character' for colored grain, and 'figure' for fiddleback. The terminology used when discussing wood can be very confusing, so below is a short explanation of the terminology I use and what I mean by it, as well as a few comments on the kinds of things to watch out for in the choice of a blank.
Alternating colors in the grain I call 'color'.
Cross grain rippling (the wrinkled wood look) caused by stresses in the tree above branches some call 'fiddleback' I call 'figure'.
At the crotch of the branch that causes figure above, I either refer to as 'feather'.
Dark streaks (predominately in English, but also in some Claro and Bastogne) I call 'mineral streaks'.
Things to look out for:
knots (branches) growing out of the side of the blank in the area that will be carved. Looking down on the top of the blank (the 2 1/2" wide dimension) the grain should run straight down the blank. But it doesn't necessarily have to. The most intensely figured sections are often close to the area of the center of the tree or involve a branch growing very nearby that may pull the grain in various directions, so some imperfections in grain flow sometimes have to be accepted.
Ideally no (or minimal) drying cracks in the wood. However, the most intensly figured blanks may have surface cracks that may or may not continue into the wood to the level of where the gunstock will be. Sometimes we have to accept these cracks and voids and fill them in order to enjoy the beauty of a massively figured piece of wood. Just remember that the most figured wood tends to have the most challenging stuff going on: wood that likes to splinter and split when carving, voids that need to be filled, etc. A perfect blank would have none of these issues, but then such a blank would probably not have the most intense figure either.
Sap wood is typically considered a negative, but sap wood is no less hard or strong than the heart wood, and can impart some interesting contrasting color in the stock while keeping it's price down. Some wood, like Bastogne and English, will have large areas of light colored wood that should not be confused with sap wood.
Grain Sweep should curve up through the pistol grip, especially in the area of the grip cap as that's an area that likes to break off if the grain goes straight across the grip cap area. Most of the grain should carry all the way from the buttstock and curve up through the pistol grip and then curve somewhat up through the forearm. If the grain goes straight from the buttstock to the forearm with no curve, just a straight grain from one end of the blank to the other, when the pistol grip area is carved you're left with wood grain that ends at the end of the action and the forearm can literally shear off of the pistol grip if dropped (or in the case of a heavy recoiling firearm shear right off the pistol grip from recoil).
Typically good grain sweep is found affordably in the middle grades. The lower grade 'straight grain' wood of course has no sweep. Higher end grades of wood approaching exhibition grade are judged first on color and figure, and if they should also have good grain sweep they will be at the higher end of the price structure. Exhibition grade wood like feather crotch may have horrible grain sweep yet are still highly prized, and a piece of exhibition wood that also exhibits good grain sweep puts it at the highest price range.
Note: there is no standard for grading terminology and pricing. Here I use common phraseology and list what I mean those terms to mean and the approximate price range such wood falls in. Prices ranges listed are for Claro. English and Bastogne are significantly more. Prices listed are also a representation of the average kinds of prices I see blanks retailing for online. My prices tend to be less for better quaility.
Standard: Wood that has no interesting color or figure. Typically Claro like this is valued at $70-$100
Semi-Fancy: Has a small amount of figure on one side. The figure might fall off through the blank so some may or may not end up in the stock. $100-$150 for Claro
A Fancy: Has good figure on at least one side that will definitely end up in the stock, and or has interesting color or mineral streaks, and the grain might sweep through the pistol grip. $150-$250
AA Fancy: Has good figure on both sides of the blank or awesome color, likely has good grain sweep. $250-$350
AAA Fancy: First level of what I call 'Exhibition' grade. Spectacular figure and/or color, and likely has good grain sweep. $350-$800
Exhibition: Maximum rareness/look. $800 up to typically $1200 for feather crotch Claro and even more for English.