With dyeing, there is always a chance of an unpredictable outcome ;-) but I think it can be done. Monte Cristo is 100% cotton and there are chemical dyes that work in cold water, giving you an option to use a big container (garbage bin, or .....) which allows for the blanket to really move around in the water to get even colour spread. If you have a bit of Monte Cristo yarn left over, I would certainly dye a sample to see if you would get a good result before moving on to the blanket. Dyeing a fluffy yarn could be a different result and it would be useful to see how the Monte Cristo behaves in a dye bath! Let us know your results!