The first number after VDU 19 is 0, which normally produces black in mode

128. The second number refers to the actual colour number 1, which always

stands for red. The VDU 19 command effectively changes the association

between the colour numbers and the actual colours:

Colour number assignments                              Actual colours

in Mode 0 (128) after using

VDU19,0,1,0,0,0

                                                                0 Black

                    0                                           1 Red

                                                                2 Green

                                                                3 Yellow

                                                                4 Blue

                                                                5 Magenta

                                                                6 Cyan

                   1                                            7 White

                                                                8 Black/White

                                                                9 Red/Cyan

                                                                10 Green/Magenta

                                                                11 Yellow/Blue

                                                                12 Blue/Yellow

                                                                13 Magenta/Green

                                                                14 Cyan/Red

                                                                15 White/Black

Similarly, white can be changed to yellow by:

VDU 19,1,3,0,0,0 RETURN

(The last three zeroes are for future expansion and they must be included even

though they have no effect.)

The same principle applies in all other modes except 7 and 135.

The teletext mode

Modes 7 and 135 are unique in the way they display text and graphies.

Commands such as COLOUR, GCOL, MOVE and DRAW do not work in these

modes. Instead, colourful displays are produced using what are known as

teletext control codes.

You may have seen teletext pages broadcast by CEEFAX or Oracle - modes 7

and 135 are teletext compatible modes.

The computer lets you produce your own teletext displays using mode 7 or 135.

These modes use very little memory, and offer a wide range of colours for

simultaneous display on-sereen. The graphics are limited but effective.

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