Remember reading an interesting post on another forum (SMML) last year to the effect that the ship might well have had a pinkish coloured deck when sunk. The deck was made out of a concrete & sawdust, which gave it the pinky/brown colour & they never had time to paint it/ apply camo.
Here is a review of a build of the Revell 1/1200th kit of her, which includes info on the paint scheme & colours used (paints are from the White Ensign Colourcoats range, but the review has colour pics so you can see what they look like)
http://www.ipmsusa.org/Reviews/Kits/Ships/Revell_1200_Shinano/Revell_1200_Shinano.htm