It has to be said that, this has never been a stumbling block for me.
My Pico 4 channel kit (supplied back in 2007) came with some coloured markers, that could be attached to each lead for convenient assigning.
After a while I did find it effective to mark each lead with some coloured tape.
The thing with having a lead dedicated to channel A, is that it will run it's life cycle before the other leads. So maybe it is wise to rotate them?
If you have coloured leads, then maybe you would be less inclined to rotate them?
Like I said previously, the colour of the basic leads, supplied by Pico has never presented a problem.
The choice is yours