"... The only thing I seem to notice with the Tradition is that many of the original bags have now faded out to a lighter blue than the original, so wonder if you would be dying the bag or using a re-manufactured one?"
Madabouthoovers:
The blue Tradition cloth bags weren't a dyed fabric in the conventional sense. It was a superficial pigment added to the surface after manufacture - like the fine powdery coating of dust on butterfly/moth wings. The pigment fell away from the material over time. If the owner ever washed the bag, the pigment bled out straight-away (even with a cold hand-wash) leaving dark blue water and a permanently washed-out bag.
You cannot successfully re-dye Tradition bags. The plasticy/nylon/polyester blend of the fabric will not take new colour dyes permanently. It'll be a slight improvement (+10%), but not much.
Replacement bags are available, but aren't up to original Kirby standards.
They're very,very expensive.
They don't have the same houndstooth pattern. Close, but no cigar.
They're a very loud 'electric-blue' colour. It looks out-of-place.
There's no felt lining strip inside, to seal the zipper.
Raw fabric edges are unfinished white, and look very unsightly.
The top hanger loop is too deep, so bag hangs droopy.
There is no Kirby® Label.
The zips are black nylon - Not blue, not aluminium.
There's no zip-concealment flaps at the sides or top.
I tried dying my original bags. All were virtually unchanged.
So I bought an expensive replacement.
Unpicked and re-made the zipper seams.
Added internal felt flaps - from the original bag.
Re-made topper loop, so bag now hangs properly.
Adjusted the internal loop so it functions now.
Added the Kirby® label from the original bag.
Having done all that; I prefer the look of the original, faded bag, to this modern, gaudy, knock-off.
I'm considering making my own from blue corduroy.