Not all the fields were gray, I believe they all were green however I didn't attend every regional or see every venue. If I remember correctly they were green and depending on the light it would look more like a greenish gray.
Granite State Regional:
http://www.chiefdelphi.com/media/photos/35102
Michigan District:
http://www.chiefdelphi.com/media/photos/35101
North Carolina Regional:
http://www.chiefdelphi.com/media/photos/35528
Although it may look cool, different carpet colors can be tough on the eyes, I mean I can't stand watching Boise State football for the following reason.
http://boisestategameday.com/wp-cont...os-stadium.jpg