sand it back and you will probably find a nice amount of colour residing in the spalt
spalt gets a bit spongy so it probably soaked it all up. i am surpirsed by the complete coverage though, what did you do it with?
having said that, every piece of spalt is different. i would do a bookcase from something like spalted beech at an early stage of its spalt but not from maple at the point where its nearly completely rotted away - take each piece as it comes