I had the same experience WW1, put three kits together back in the early eighties, a rifle, a pistol, and a shotgun. They came out great, and still look nice, though they have darkened some. Last summer I built a .32 flinter, and the browning came out blotchy. This winter, a built a Trapper Pistol kit, and while the browning looked better, it was still not like I wanted it to look. I completely stripped the flinter again, degreased with acetone, followed by Birchwood degreaser, and came out with worse browning than the first attempt last summer. Like you, I thought they must have changed the formula. I still had a .54 Mountain rifle kit to build, so I bought a hobby gunsmithing book of ebay. It has a pretty good section on blueing and browning. The browning woes are caused by the new chemicals being used in city water. he says well water is better, but it is best to use clean rain water or distilled. I just got done browning the .54 yesterday, and the author seems to be correct. This one came out nice, and I plan to redo the other two using his methods. They are as follows.
1 polish the metal with sandpaper, ending with 180 grit.
2 degrease with any degreaser (I used acetone followed with Birchwood).
3 grease bore and seal with wood plugs driven into bore.
4 rinse in clear water.
5 put two steel wire hangers in your steel barrel tank so the barrel (and under rib) is one inch from the bottom, and hang small parts from wires so they are the same one inch from sides and bottom. Cover the parts, at least an inch, with rain or distilled water, keeping track of amount. Add 1/2 tablespoon of lye per gallon of water and bring to a boil. Boil for twenty minutes. From this point on, do not touch the metal without rubber gloves.
6 remove from lye water, and place in hot (180 degree) water for two minutes.
7 remove from rinse, dry, and heat barrel just to the point water sizzles on it. Do not overheat, or you will get too much slag and the color will be too dark. apply more heat whenever sizzling quits. When completely covered, set aside for 15 or 20 minutes until you can handle it comfortably.
8 While the barrel is cooling, warm the rinse water back to 180 degrees. place barrel back in the rinse water and card slag lightly with degreased steel wool. I rinsed mine with acetone and boiled it in the lye with the metal, then rinsed again with distilled water.
9 repeat 7 and 8 until you get desired color. I got the "plumb' color I like with three applications. I also changed rinse water each time.
I don't know if all this is necessary, but it worked well, so I plan to keep doing it this way. I hope yours comes out as nice as this one did, and I hope to get the same results on the rifle and pistol when I redo them again.