I had the same problem a couple months ago. Check your connections. After checking the connections from the monitor to the tower I found they were loose. Tighten the connections that are loose and you should then have color again. Good luck
After reading many ways to handle this problem I found that they all referenced color filters and that they need to be turned OFF so I searched Settings which took me to ease of access, vision, and color filters. As soon as I changed the the indicator
to OFF I had my color back. Hope this helps some other person.