Crust discoloration

Hello all , I am a new baker hoping to start making larger quantities in the near future but I've had a problem today that is going to keep me up this evening baking for an event tomorrow.

I used the Ciabatta Poolish Version (which I made from Bread Bakers Apprentice)

I tripled the amount, had it ferment 3-4 hrs before putting it in the fridge overnight around 10am I pulled it outand used a warm stone on a lower rack of the oven as a proofer for an hour

I did the stretch and fold , let it rest 30min and then waited 1.5-2hrs turned the oven on and loaded it with pans to maximize space. I had my stone and a small bread pan that would sit next to it using up the bottom rack, and on the top rack I had two cookie sheets flipped over

I then put 3 loaves (in an epi shape) on each level

Main problem is they didn't brown out right, they become fantastically dull and they began burning before getting darker. 

I usually cook at 500 but I took it down to 400 on the next batch to see if it helped no bueno, I took the top row of sheets off and flipped one over to get more hot surface to create the steam blast but no bueno

This is just puzzling to me I am wondering: a. Did I overproof? b. Did I overcrowd the oven and cause bad circulation? c. is it just using the ciabatta recipie that made the difference (the crumb was great but the crust looked ancient) Any trouble shooting would be much appreciated. I picked the recipie because last time I used it (in the ciabatta form) it tasted great and maintained for several days. There is a party on soon that I'm serving bread at and I was trying to get it down by then, all pretty and such (maybe I'll have to use the ol' Bertinet standby after all)

Thanks in advance