It will partly depend on what kind of colouring was used on your living room blocks. If it was a water-based or spirit-based stain it will have penetrated into the wood and it will be very difficult to bring them back to their natural colour. If, on the other hand, they have been treated with coloured varnish you will probably be able to strip that and be in with fighting chance. It will be hard work and probably a long job, but I'm sure you'll think it worth it. I'd try a little patch where it won't show with a paint stripper such as Nitromors to see what happens. If it's varnish stain it'll bubble up and you'll be able to scrape it off revealing the natural wood; if it's clear varnish over woodstain the varnish will lift but the colour will remain. If you can get the wood back to natural, steel wool and white spirit work well to give it a final clean. To expose a fresh surface of natural oak ready for clear varnishing, a floor sander is the best tool - but PLEASE be careful. Floor sanders can be vicious brutes and the last thing you want is to sand great grooves and hollows out of your lovely oak floor! You CAN do the job by hand, but it's a long, long, hard, tiring job - not unlike holystoning the deck of a tea-clipper! Best of luck.