The yellow/white wire is for speed sensitive volume control I think, and blue/grey is DEFINITELY the dash illumination wire.
By 'memory' do you mean permanaent live? If so it will be the red one

If you want ignition live you'll have to run one from the fusebox, or from the fan switch. If its an early MK2 this is dead easy as on the rear of the fusebox you have 2 groups of spare spade terminals, ons side live, the other ignition live.
If its a late MK2 think about wiring up the 'key in ignition' feed, its there but hardly ever used. The correct wire is labled up as 'S' I believe, or perhaps 'SU'. The way I did it was to chop a plug off a scrappy car, and remove one of the wires. I then fitted one of the wires to the empty slots in the MK2 plug & used trial & error with a multimeter till I found the key in ignition feed, then ran it to the radio using a fuse.