* 100% became #F
On an actual Amstrad CPC, the 50% half-intensity colour signal is measured closer to 40%, not really 50%. [https://www.grimware.org/doku.php/documentations/devices/gatearray#inkr Source]
This is why the Amstrad engineers chose #6 for the 50% value instead of #7, to better match the real Amstrad CPC palette.