C - Change colour to the next one from the cyclic sequence: black, blue, green, cyan, red, magenta, yellow, and white.
F - Move forward by one cell and paint the new cell.
R - Rotate clockwise by 45°.
[ - Begin a repeatable block and continue executing subsequent code normally.
] - Go back to the beginning of the current repeatable block, repeat it once more, and exit the block. A block bounded by ‘[’ and ‘]’ behaves like a loop that runs twice before the block exits.
[FFF] - Draw a column of 6 white cells.
CC[[FFF]] - Draw a column of 12 blue cells.
CCC[[[[[FFF]]R]]] - Draw a green octagon.