Teletext is mostly known usage in conjunktion with broadcast television. Many television sets have an integrated teletext viewer. It's a particular form called World System Teletext which defines the size to 40x25 characters, of which the first line is used as a header. This standard is supported by abydos up to level 2.5.
Teletext uses a rudimentary palette with full bright colors. Exactly how the graphics is rendered may vary depending on implementation. From blocky bitmap fonts to smooth ones on more recent television sets. Among teletext artists there seem to be a preference for blocky fonts, but as far as I can tell no particular one. There are also variations in aspect ratio, HD television sets tend to stretch the image to (or closer to) HD 16:9 aspect ratio. Also palettes with lower saturation occurs. But abydos renders the image with a supposed 4:3 ratio, the original palette and a blocky font.
The Teletext palette.
This is what a rendition looks like with the current version of abydos.