One of my first game industry jobs was to take a Commodore Amiga game called Rock N' Roll (by Rainbow Arts) & convert the graphics to work on the Atari ST, Spectrum and Amstrad-CPC home computers.
The Amiga has twice the colours of an Atari ST so my first job was taking the 32 colour Amiga graphics and making them work in 16 colours. This was harder than most typical Amiga to ST conversions because the gameplay requires the player to find four different coloured keys, to unlock four different coloured gates. So out of the 15 usable colours in my palette (colour 0 is always kept as 'transparent') I needed to have enough colours to depict four different coloured key and gate combos.
Amstrad CPC version was better as far as colour went. It has a fixed palette of 26 colours, that though gaudy, have enough distinct colours to represent the key & gates
The Spectrum is a monochrome machine (per 8x8 pixel block anyway) so that required graphic symbolism for the key & gates