Photoshop :: Redo Image?

I'm on a roll, folks...have been browsing this forum madly since I stumbled across how to included images in my message, so I can't show you the image, but I was wondering if anyone would know how to get an image into one colour.

It sounds simple (and I'm sure the solution is), but I've got an image that's maroon and grey and has LOTS and LOTS of cross hatching etc, so changing it to black with the wand is a nightmare and, the crops are so close that you can barely differentiate lines.

I've changed it to greyscale, but that turns the maroon lines and squiggles terribly, terribly light, like a low-res print out. Is there any where to do, essentially, a search and replace on a colour? Simply turn all the maroon, no matter how squiggly it is, to black or should I clear a week and do it manually?