chromogen
noun
chro·mo·gen ˈkrō-mə-jən 
1
: a precursor of a biochemical pigment
2
: a pigment-producing microorganism
Example Sentences
Recent Examples on the Web Whitening agents, which tend to be bleaching chemicals like carbamide peroxide or hydrogen peroxide, break up the chromogen so that it can be easily washed away. 
Sarah Jacob, SELF, 13 Aug. 2021
Sarah Jacob, SELF, 13 Aug. 2021 Word History
Etymology
chromo- + -gen
Note: Term introduced by the Scottish chemist Thomas Charles Hope (1766-1844) in "Observations and Experiments on the Coloured and Colourable Matters in the Leaves and Flowers of Plants," a communication read on March 21, 1836, to the Royal Society of Edinburgh and published in the Society's Transactions, vol. 1, no. 6 (1836), pp. 126-28.
First Known Use
1858, in the meaning defined at sense 1
Medical Definition
chromogen
noun
chro·mo·gen ˈkrō-mə-jən
1
a
: a precursor of a biochemical pigment
b
: a compound not itself a dye but containing a chromophore and so capable of becoming one
2
: a pigment-producing microorganism
many bacteria are chromogens