I've have really noticed that UV can do very strange things in particular to dark shades of greens and browns - repeatedly. At least the type I used to use did. Just a suggestion, but if you have already tried it without your UV and its still not good - try a good block dye like French dye blocks - yes, the hunter green would be my first choice too. "Army" green to me means olive - so maybe the palm you are using is just particularly succeptable to yellowing - and in that case try a different one - or, if you get good results right upon unmolding, but THEN they yellow - try a different UV. I did some large WHITE palm forever pillars many months ago and gave them to someone who kept them by two windows on her mantle - and they are still bright white and I did NOT use UV. Thats why I mention maybe its the palm itself.