The EP Colour Standards were originally visual colour standards intended to improve colour communication between sites by defining a sample colour as being close to a physical liquid standard ("near EP Y2") rather than using the words "light yellow".
EP consists of 3 primary colour standard solutions (yellow, red, blue) that are combined with hydrochloric acid to make 5 standard solutions that when further diluted with hydrochloric acid (10 mg/l) make 37 reference EP standards; Red (R1 - R7); Yellow (Y1 - Y7); Brown (B1 - B9); Brown/Yellow (BY1 - BY7); Green/Yellow (GY1 - GY7).
The procedure for manufacturing these standards is time consuming and tedious and the stock solutions must be stored in a cool dark place in order to remain colour constant. It is for these reasons that standards of a more stable nature were in demand. Thus a series of Lovibond® colour discs were originally developed to represent this scale.
An alternative to the visual methods is now available as a program in the Lovibond® PFX and PFXi ranges of spectrocolorimeters. Measurements are based on a comparison of CIEL*a*b* values for the samples to saved values for the EP standards (US and Chinese Pharmacopoeia are local alternatives.)