Key words are printed in uppercase when the program is output with "list". But entering code is usually done in lowercase.
line 10: screen mode 0 is used (16 colours; 20x25 characters)
lines 20/30: set up colour palette; note that multiple instructions can be combined on a line
lines 40 to 70: a "for" loop over i
line 50: set the paper (background) colour to i
line 60: print 40 spaces (= 2 lines); space$ is a built-in function that returns a string
When the program ends, the "Ready" prompt is white-on-black because the current foreground (pen) colour, which is 1, had been set to white ("ink 1,26"). The background colour is 8 after the loop and "ink 8,0" had set that to black previously. See File:Amstrad CPC ink numbers.png for a chart of Amstrad ink numbers.