336 A DICTIONARY OF COLOUR
c Robin’s egg blue
A light greeny blue colour with brown flecks resembling the egg of the Robin
and used as a ceramic glaze.
n roccellin
A red coal-tar colour used as a dye.
n rods
Rods are extremely sensitive cells at the back of the retina of the eye which absorb
light – each human eye containing 120 million rods. Rods contain the pigment
rhodopsin and respond to dim light whereas cones are less light sensitive and
respond only to brighter light. When light reaches the rhodopsin the molecules
of the pigment release a chemical which transmits a message to the brain. As
sunlight gradually replaces night the cones slowly replace the rods as the receptors
of light. We experience this adjustment in our vision (called the ‘Purkinje Shift’
after the physiologist J E Purkinje (1787-1869)) when going into sunlight from a
darkened room (and vice versa). Rods are sensitive only to light so that we cannot
see colour when it is dark.
a Roman
As applied to colours and pigments such as Roman ochre, Roman Lake and Roman
Brown.
c Roman Brown
A copper colour also called Hatchett’s Brown.
pr ros- (L)
Rose.
n rosacea
A chronic form of acne in which the nose becomes excessively reddened. In
advanced form it is called rhinophyma.
n rosaniline
A red dyestuff derived from aniline known as magenta.
c rose
A light crimson colour or red; pink.