[jamesgeck0]

MX blue and brown keys also require slightly less force to press than a rubber dome key.

[melling]

From the keyboards subreddit:

Red (45 centiNewtons, 60 cN)

Brown (45 cN, 60cN, tactile)

Blue (50 cN, 65 cN, click/tactile)

Black (60 cN, 80 cN)

Clear (65 cN, ?)

Green (80 cN, 105 cN, tactile)

http://www.reddit.com/r/keyboards/