Did the sensitizer turn dark after use, or without use.

If you tray sensitize, the sensitizer will not keep after using it. Any organic material (paper, gelatin, dust, etc) will react with the dichromate, turning it brown.

I have had Ammonium dichromate react with rubbing alcohol and turn dark -- from impurities/additives in the rubbing alcohol most likely. It is one of the reasons I use acetone when brush-sensitizing.

The sensitizer when stored in the fridge can have some of the dichromate fall out of solution -- usually will go back into solution once warmed back up.

Odd that you need a more contrasty neg for 1% -- the weaker the solution, the lower the contrast you need in the negative -- 1% should be good for negs of relatively low contrast -- one that makes a decent silver gelatin print with perhaps a #2 VC filter.