I have just started and have not gotten further than the letters yet, so I might not be the best adviser... but according to the "russian language helper" in the links here, I think it sounds like a "ö" in Swedish, or eu in french, but more... hm, how to explain, as though your throat is less open, as if your about to cry :) . or perhaps as if trying to sound cute, as when some people talk in an annoying way to children.
I am not sure it is right (as I don't really have any knowledge in russian at all) but if I imitate that sound, the tongue sort of blocks part of the throat, while the sides ot the tongue is on the sideteeth, like a tunnel, and the tip of the tongue touch the "root" of lower front teeth).
Hopefully someone with better knowledge can give better advise.
ok that was wrong I think, looked at that page agian, and the examples where they use the letter does not sound the same as the way the letter is pronounced on its own... or does it sound different in different contexts?
In the word for 4 and the colours I think it sound quite a lot like a "i" (not "aj", but as in sit, but much longer and somewhat throatlike, or something)