I'm going to honestly step out and say I've never had to take these colours into consideration, but I think these would be extremely helpful for newcomers. I have personally never needed to PM a moderator, or Global Moderator, on a problem (I think) but for those needing to, this would be extremely helpful. My personal favourite is the Cyan/Purple combination :3 smooth, close fitting, yet easily distinguishable from each other, all while fitting to the colour scheme!
I love your idea ;3