I'm not color-blind, but as i see it, the main issue here is that you have two icons, neither of which obviously has more emphasis than the other, and which might not be easy to distinguish if both weren't on the screen at the same time-- it's the same jewel, unless you observe it carefully, you wouldn't know if you are looking at a page of posts all of which you haven't seen, or all of which you had.
1) A brighter jewel, but one with less saturation
2) A darker jewel, but with more saturation
So both get about the same amount of emphasis in different ways
if for instance, the "unread" jewel was vibrant blue, and the read one was nearly grey, it would be intuitive which was which. For even greater usability, there would be some sort of difference in the form. Lots of other ways to make the distinction more obvious are possible too...
thread.png
Those forum icons are on my screen extremely close.
Thanks.