The colors selected by the artists had a direct bearing on the characters portrayed. According to ancient texts, there are three broad qualities assigned to superhuman, human, and sub-human beings, viz. Satva (the noblest), Rajas (the active and middle principle) and Tamas (the dark and destructive principle) respectively.
To represent Satvic quality, green and shades of green were used. Characters of the Rajasic quality were portrayed in red or golden, and the Tamasic nature of the gods were represented not by black but in white, while demons and demonesses were represented by black.
Among the subjects, Vishnu and his Satvic incarnations, Parvati, Sridevi, Arjuna, pious beings like Prahlada and Markandeya were always painted in green. Bhoodevi (Goddess Earth), Ganga, Ganesa, and the four-headed Brahma were [typically] painted in red. Vishnu was [also] painted in different colors according to his attributes.
It is true that the figures of the murals have the external likeness of men and women; but the divine, or the supra-human aspect is also obvious in [virtually] every detail. The creators of these pictures had no doubt undergone rigorous mental disciplines, or sadhana.
They had the creative skill to fill every available space with as many details as possible, and also the skill to pinpoint one or two essential details and leave the rest to our imagination. The painting in the Mattancherry palace of Krishna holding the Govardhana aloft for example, is a typical example in which minute details of the wooded mountain are elaborately depicted. This tendency to detailed elaboration is also a characteristic feature of the Koodiyattom, the ancient temple theatre of Kerala. Another later, but frequent characteristic of the murals of Kerala are the beaded or decorative outlines, not only around each panel but also around individual figures.
During the 15th and the 16th centuries, when the Bhakti movement swept through Kerala, many were the excellent murals that were painted. It is also highly probable that the leading names of the movement like the eighteen and a half poets of the Zamorins court, Ezhutachan, Melpathoor, Poonthanam, and the venerable sage Vilvamangalam could have been instrumental in reviving this popular tradition of religious art.
The decay of this tradition that started in the late 18th century, gained momentum with the Mysore invasion of Malabar (1766-82) and the take-over of the Travancore temple trusts by the then British Resident (1811). The final blow came when the portrait style of painting of Raja Ravi Varma (1848 1906) gained fame and popularity.