Acura and Honda: Usually on a label inside the drivers' door jamb, if you don't see it look on the passenger side door jamb.  See diagram below.  The highlighted part displays the color code.  The code should begin with a letter and can contain letter, numbers and dashes.  The typical color code format is "NH-583M" or "B89P" which corresponds to "Vogue Silver Metallic".
  

Audi and Volkswagen: Usually hidden around the spare tire on a paper tag and can often be loose or folded over.  Can also be found under the dash.  Usually shown as a four digit code, though it is possible that there can be a two digit code instead of or in addition to the four digit code.  Either code is correct.  The typical color code format is "LD7X" or "R2" which corresponds to "Platinum Grey Metallic".

BMW and Mini: Usually under the hood by the strut towers. The code should contain three numbers and sometimes have a slash followed by a fourth digit.  The typical color code format is "300" which corresponds to "Alpine White III".

Buick, Cadillac, Chevrolet, GMC, Hummer, Oldsmobile, Pontiac and Saturn:  GM has a confusing color code system.  On all trucks, the sticker is located in the glove box.  On other vehicles, check the passenger door, the glove box, drivers' side door jamb, middle console, the spare tire cover or under the trunk mat on a label.  Should be a three or four digit code ending in U or a WA number that is four digits long.  The typical color code format is "51" or "WA316N", which corresponds to "Slate Grey Metallic" and is usually preceded by BC/CC.  So you would see BC/CC 51 or BC/CC 316N

Chrysler, Dodge, Jeep and Plymouth: Usually found on the drivers side door jam.  Can also be found on a metal tag in the engine bay on the radiator support, the firewall or fender well.  The code should be three digits.  The typical color code format is "BS" or "GBS" which corresponds to "Deep Water Blue Pearl".

Ford, Lincoln and Mercury:  Always on a label inside the drivers' door jamb.  The code should be two digits, normally two letters or a letter and a number.  The typical color code format is "WT" or "M6640" which corresponds to "Performance White".  However, you will almost always see the two digit code.

Hyundai: Usually on a label inside the drivers' door jamb.  Other places the code may be found are inside the engine bay area by the firewall, the radiator support or under the drivers' seat. See diagram below.  The code will be two digits.  The typical color code format is "3E" which corresponds to "Blue Onyx Metallic".  Some later Hyundai's use a three character code.  The sample plate below shows the paint code S3, which is the same as S3B. 

Infiniti and Nissan: Usually located on the drivers door jamb.  Codes normally have three digits and sometimes displays a fourth digit.  See diagram below.  The typical color code format is "AX6" which corresponds to "Redline".

Jaguar: Usually on the drivers' door jamb, but in older models, it can be found under the hood, trunk, etc.  Codes are usually shown as a three or four digit number.  The typical color code format is "1957" or "HGZ" which corresponds to "Jaguar Racing Green Pearl".

KIA: Usually found on the front of drivers side door jamb.  Codes are usually two digits long.   The typical color code format is "B3" which corresponds to "Mica Blue Metallic".

Land Rover: Usually on the drivers' side door jamb or under the hood.  Can also be found inside the engine bay area by the firewall, by the radiator support or the passenger side door.  Codes are usually shown as a three digit number.  The typical color code format is "LRC961" or "HAF" which corresponds to "Epsom Green".  You may see either format, both refer to the same color.

Lexus, Toyota and Scion: Usually on the drivers' side door jamb.  See diagram below.  The color plate it will have the letters C/TR and then the paint code follows.  The typical color code format is "C/TR 3P1 FA09".  The color code is 3P1 and the FA09 has nothing to do with the color code, this color code corresponds to "Impulse Red Metallic".

Mazda: Usually on the drivers side door jamb, but in older models, it can be under the hood, trunk, etc.  See diagram below.  The typical color code format is "21R" which corresponds to "Moonlight Gray Metallic".

Mercedes: Located by the radiator crossover or support bar, or the drivers side door jamb or the engine compartment adhered to the underside of the hood.  Code is three or five digits long and contains numbers only.  Older models may have a prefix of DB followed by a three digit number.  The typical color code format is "373" which corresponds to "Atlantic Blue".

Mitsubishi: On a metal tag inside the engine bay on the firewall or on the drivers' side door jamb.  Can also be found under the dash.  The code should be three digits, always starting with a letter.  See diagram below.  The typical color code format is "R71" which corresponds to "Passion Red".

Porsche: Usually around the spare tire, but can also be found on the driver side door jamb, under the hood, trunk, etc.  The typical color code format is "LD7X" or "2R" which corresponds to "Platinum Grey Metallic". 

Saab: Usually found on the drivers side door jamb.  Can also be found underneath the hood by the strut towers.  Codes are usually shown as a three or four digit number.  The typical color code format is "230" which corresponds to "Scarabe Green Metallic".

Subaru: Usually underneath the hood by the strut towers.  Should be a three-digit code, with the first two digits being numbers (the third may be a a number or a letter).  The typical color code format is "49B" which corresponds to "Slate Grey Metallic".

Suzuki: Usually found inside the engine bay area by the firewall.  Also look on the front of the drivers side door.  Codes are usually three digits long.

MAKE OF CAR	LOCATION (see drawing)
Honda	6
Hyundai	3 or 6
KIA	6
Lexus	6
Mazda	12
Mitsubishi	2 or 3
Nissan	2, 3 or 9
Toyota	6