Here is some of the differen't colours and markings in rats.
Click on the image for a larger picture.
Himalayan
Rex 
Bella's Bellamy
Hooded
Mette's Dino
Pearl
Mearl 
Bellas Reznor
Roan
/ Husky 
Jorunn's Nikita
& Izabel
Siamese
Corina &
Walter's Lancelot
Blue
Point Siamese 
Estelle's Harvey
Colours:
Agouti
Bella's Toby
Beige
Jorunn's Jazmine
Black
standard 
Bella's Kenny
American
Blue (Dumbo) 
Estelle's Angel
Blue
Self (Dumbo) 
Bella's Isabella
Powder
Blue 
Estelle's Silvey
Champagne
Bella's Lenora
Chocolate
Rex 
Jorunn's Curlz
Cinnamon
Rex 
Snuffy
Silver
Fawn ( Dumbo) 
Bella's Malachai
Russian
blue (Rex) 
Estelle's Ivor
Pink
Eyed White (PEW) 
Bella's LeStatt
Black
Eyed White (BEW) 
Mettes Claudia
Hairless:
Hairless
(PEW) 
Bella's Ruby
Hairless
Dumbo 
Bella's Martin
Here you'll find links to other great websites who show the differen't colors, markings and coats in rats:
http://www.angelfire.com/sd/silverstone/kleuren.html
http://www.ratweb.fsnet.co.uk/myrats.htm
http://www.hawthornrats.co.uk/varieties/varieties.html
Rat & Mouse Club of America (RMCA)
http://www.rmca.org/Standard/Rat/#organization
http://mutantspud.com/frc/learning/markings.htm Markings
http://mutantspud.com/frc/learning/colors.htm Colors
http://mutantspud.com/frc/learning/coats.htm Coats