Coloured coating within CRT
It looks like rings with graphite between an algae green  silicate binder to dissipate static build up on the tube to prevent glass partial discharge. If discharge occurs between ring  of dielectric, the capacitance is in series and only a partial discharge would occur if it failed from contamination in the vacuum.  A conductor then bleeds the mA current off somewhere.

Aquadag™ consists of a dispersion of colloidal graphite in distilled water.

The aquadag coating has two functions: it maintains a uniform electric field inside the tube near the screen, so the electron beam remains collimated and is not distorted by external fields, and it collects the electrons after they have hit the screen, serving as the return path for the cathode current

In some CRTs the coating performs a third function, as a filter capacitor for the high-voltage anode supply. -||-||-||-||- &lt; 1nF max.

Aquadag™ brand is now owned by Henkel.