139 Run the program. This will fill in one half of the square. Now add: 170 PLOT 85,800,400 Run the program and the whole square should become red. How to change colours At any particular moment the computer can print and draw on the screen using four colours. This page uses two ‘colours’: a white background colour and a black foreground colour – that is, black writing on a white background. Similarly, the computer has a text background colour and a text foreground colour but, in addition, it is aware of a graphics foreground colour (used to draw lines), and a graphics background colour. When you change MODE the computer resets all these colours as follows: – Text foreground colour:
white – Text background colour: black – Graphics foreground colour: white – Graphics background colour: black The number of colours that can appear on the screen at one time depends on the MODE selected. In MODES 0 , 3 , 4 and 6 you can only have two colours at any time and they are normally black and white. In MODE s 1 and 5 you can have up to four colours at any time and they are normally black, red, yellow and white. In MODE 2 you can have up to 16 different coloured effects. Let us consider MODE 5 for a moment and explore the effects that are available. MODE 5 is a four colour mode and the default colours are black, red, yellow and white.
As you may have gathered, text and graphics are dealt with separately so to change the colour that will be used for text output type COLOUR 0 To give black text COLOUR 1 To give red text COLOUR 2 To give yellow text COLOUR 3 To give white text However, to change the colour used for graphics, for example to produce lines with the DRAW statement, you use these statements GCOL 0,0 Black graphics GCOL 0,1 Red graphics GCOL 0,2 Yellow graphics