Which source of a natural dye is used in pH paper?

'Litmus' is a water-soluble mixture of different dyes extracted from 'lichens'. It is adsorbed onto filter paper to produce one of the oldest forms of pH indicator or pH paper. A 'lichen' is a composite organism that 'algae' or 'cyanobacteria' living among filaments of multiple 'fungi' species. 'Lichens' come in many colors and are not plants. 'Litmus' can be found in different species of 'lichens'. The 'roccella tinctoria' is a lichenized species of fungus in the genus 'roccella'. It was first described by Augustin Pyramus (4 February 1778--9 September 1841), who was a Swiss botanist.

The main use of 'litmus' is to test whether a solution is acidic or basic. Blue 'litmus' paper turns red under acidic conditions and red litmus paper turns blue under basic or alkaline conditions, with the color change occurring over the pH range 4.5-8.3 at 25 deg (77 deg F). Neutral 'litmus' paper is purple. Wet 'litmus' paper can also be used to test for water-soluble gases that affect acidity or alkalinity; for example, ammonia gas, which is alkaline, turns red 'litmus' paper blue. Also, chlorine gas turns blue 'litmus' paper white as the 'litmus' dye is bleached. All of the chemical components of 'litmus' are likely to be the same as those of the related mixture known as 'orcein'. This is also a major source of 'roccella tinctoria'. 'Orcinol' is extracted from 'roccella tinctoria'. It is then converted to 'orcein' by ammonia and air. 'Orcein' is a reddish-brown dye.