Hi Edubarca
I am not sure why you are using CMYK with a laser printer yet if you have the option to change your workflow to RGB, I suggest just staying in sRGB.
Independent fo the above comment, your gray color is simply blue and it is noticeable. If you wnat a good match to gray, the color needs to be gray and not off gray as a starting point.
There are many ways to correct this yet I masked off the color areas and then coverted the rest of the image to B&W (e.g. a B&W adjustment Layer is just one approach
In the image below, your original is on the left and the corrected version on the right where the blue is no longer included in the grey area.
To get good colors both the monitor needs to be color calibrated with a hardware device such as from Xrite or Datacolor, and printing has to be done with the correct settings in the printer device driver and settings in Photoshop. It is not commone for laser printers to come with ICC profiles yet that would provide the best match.
I suggest starting with removing the blue from your gray tones and if that is not adequate, we then proceed with tracking down your color management issue (and if possible using the sRGB color space and not CMYK)
Just my opinion of course
John Wheeler