Jeff: I believe your khaki belt with the sewn on cartridge loops and riveted 'end-plates' (with 'closed' wire-bails), is actually a Hurburt manufactured cartridge belt.
From my understanding, Spaulding belts were lighter canvas with sewn on cartridge loops and the cut ends were protected with a sewn on leather 'beading'.
As Dick Hosmer suggests, the 'woven' cartridge loops were a patented/proprietary process owned by Mills and only used by them.
Of course, reproduction belts started being made in the late 1950s and some of these may have had woven loops.
FWIW - The fading of your blue belt looks pretty correct for an original Mills belt.
I have a Hurlburt, 50-round 'sewn-on-loop', .30-40 belt that started life as a khaki belt and was later Dyed blue. It has faded to a 'purplish - blue'. On the back, in black ink stenciled lettering, it is marked: "Co. M 2nd N.Y. 99". It is also stenciled "34" in white paint, which possibly could be a Michigan regimental number applied after Dying.
This belt has the unmarked riveted end plates, with 'closed wire bails'. There are two heavy sheet brass keepers to keep the belt neat and flat. The belt is buckled with a heavy wire "C" closure.
The color (and time period) of U.S. canvas belts is a bit of a mystery to me.
FWIW - From my viewing of Michigan unit pictures:
I notice khaki, '45-loop' (.45-70 belts), in the photos of the five Michigan regiments assembled in 1898 at Island Lake, Brighton, Michigan, to be sworn in for Federal service.
In the 1899-1903 period, Michigan troops have model 1899 Remington-Lee rifles. Their Mills belts are dark blue with special pockets for spare Lee magazines, as well as, cartridge loops. (It is possible blue Dyed belts were also in use for uniformity).
Family pictures I have, from around 1903-04, show Michigan Guardsmen with khaki .30-40 belts and Krag rifles.
