I have a Samsung SP-55W3HF and today a blue shadow

Sounds like the same problem that has occured in the Hitachi Ultravision projection TVs and nearly every other brand of TV with a light engine.. Is it a blue blob in the middle or a shadow across the top of the screen? If so, the light engine is bad. If you are handy you can do it yourself in about an hour or two. If not, you'll have to take it to a repair shop. The cost will be about $400 for the engine and another $200 or so for the labor.....I'm estimating. Hitachi knew the light engines were bad in their TVs so even if it is out of warranty they provide the part for free so long as you bring it to an authorized repair facility. Call Samsung and see what they say and search the internet for Samsung light engine problems.

It sounds like a convergence issue. Are you able to try the convergence built into the tv? If that doesn't work you will need to have a professional come out and align the color guns. Also it is always possible there is a more serious problem with internal components. If you need help finding a qualified repair tech. in your area let me know.
Thank you,
Lee