Try diluting your solution with distilled water, applying a thinner layer of agent, or cutting back on the humidity while rusting. If none of this works,[and it should], try Pilkington's. I've had no problems getting yellows, browns, or reds, if I slowed the rusting process a bit. Even with Laurel Mt., which is quite aggressive.
You mention "before boiling". I'm going to ask a dumb question. You're not boiling your "brown" barrels?
Jim