If I were to design my own teletext pages, I feel that looking at existing examples of good design is necessary to get some inspiration.
This design, from a German teletext page, makes use of the bold white on red and blue on yellow. Interesting to note that some aesthetic decisions are based on colour contrasts: for example red on yellow might be too much of a clash, whereas yellow on red is deemed to be fine. The blue on red isn't quite working though, and the purple on yellow doesn't show up all that well.
This colour scheme of red on white works better but the blue and red areas are staring to clash once more. Only on teletext could a designer get away with juxtaposing two such strong colours. Pixel mapping, an often underused technique, is also used here to render the Sky Box Office logo.
The above screenshot from Ceefax in 1983 is crowded but that's part of its appeal. Trying to stuff as much information on a page as possible is a trademark of the early teletext transmissions - mainly due to the high cost of having a larger number of pages (£50 per page when Ceefax began).Another crowded page, this time from the commercial service on Sky. I like this because there's a lot going on at once: aside from the main focus of the page - the weather forecast - there is room for an advertisement and a premium rate phone number and even some index links.
Screenshots from Teletext then and Now