According to News18, the Directorate of School Education in Tamil Nadu had recently warned of action against schools where children had to wear wristbands of different colours based on their caste. It had asked senior officials to identify schools taking part in this practise, and also what action had been taken against them.

Source: Newindianexpress

The wristbands come in shades of red, yellow, green and saffron indicate whether the person belongs to a 'lower class' or 'upper class. Rings and forehead tilaks are also apparently used as caste markers.

The matter came to attention after a circular issued by 180 trainee IAS officers that said,

It is informed that the officer trainees of IAS 2018 batch lodged a representation to the Government where it has been stated that in some schools in Tamil Nadu, the students were made to wear colour coded wrist bands. These practices are supposedly being used for sports team selection, reassembling during class and lunch intervals. Allegedly, these practices are enforced upon students themselves and supported by influential caste persons and teachers.
Source: Indianexpress

Social activist Evidence Kadhir claimed that the problem has been going on for a while, saying,

It’s not just the coloured bands. In government schools where midday meals are provided, students from the oppressed community are asked to bring their own plates.
Source: Newindianexpress

However, school education minister KA Sengottaiyan said on Thursday that he had asked all education officials not to implement the circular warning acting against these schools. He told The New Indian Express,

Whatever practice exists in Tamil Nadu shall continue the way it is.
Source: Newindianexpress

Sengottaiyan claims the circular was issued without his knowledge. He labelled the circular ‘unnecessary’, and said it was passed ‘just to spark a controversy’.