Teac Tascam series 3 mixer knob Mystery

This has confused me no end and if anyone can answer me I would welcome the message

I have had a few series 3 mixers and they have all had the same multi-coloured knobs.

This 3 came in with all black knobs, the knobs 100% are from Teac as labelled TEAC 158-B-1 on the skirt.  maybe it was a special or a very early sample model.

Maybe someone changed them.

The knob looks like ones that are used on their Tape recorders.