Dense Loaf (moist) & Crumb is not White

So I have been playing with recipes and modified a no knead to the following.
3.5 cups flour
1.5 warm water
1tsp active yeast
1 large tbsp sourdough starter
1tsp salt
curls of marble cheese
process:
Let sit for 4 hours, then refridge overnight.
Turned it once and added cheese then back in freidge for 5 hrs
taken out of frdige and placed in a round cake tin to proof.
It might have over proofed as i left it unattended (at work) where by the plastic wrap was holding back the dough 
from further rise.
I put another tin on top of the cake tin (dont have a dutch oven so I was creating my own)
Baked at 475 for 30 min
then 15 min with lid off.
results as you can see. Tastes great could have used more cheese! But not spring in the oven the top was flat but it was fully expanded all around. The loaf is moist but not a fluffy white which is what I would like to get.
I am thinking no kneads dont get fluffy white?
Any ideas? Cheers