So what colors would be preferable? I personally like the green and gray, they are intuitive to me in their meaning (whereas red conveys "halt! you are not allowed!" more than "nothing new"), but we can change them if a consensus is reached...
It should be noted that there are 2 different "green" icons - 1 is "bright" green to denote that there is a new post in the board; the other is "dull" green to denote that there is not a new post in the board itself, but there is a new post in a child board. If the real problem is with the "dull" icon, we can drop that functionality and go back to a 2-icon system...