@Martin > I'm having a little trouble understanding your points.
1) The 3/4 and 1/3 isn't "greyed out", its just in a different colour so its still accessible but its highlighted to show that its not a common "on-beat" choice.
2) If you are in a loop and want to half or double the size of the loop, you can press the left and right CUE / LOOP arrows just above the jog wheel, to the right on the Nexus. On the MK1, you can keep pressing the Loop cutter to half the size of the loop. Press and hold the OUT ADJUST button while pressing the loop cutter and you'll start doubling the size of the loop.
3) Its not possible to change the colours without using rekordbox.
4) The on-air display is a ProDJ Link only function.