You may have already seen this about dichroic from A&A Products or others. There is a test strip near the bottom of the page.
http://www.aaproducts.com/DICHROI-TECHNICAL-INFO.html
You should expect the shift. If you want green, start with yellow. If you want light blue, start with pale green.... Like Kevin said there is variation in coatings from sheet to sheet. There is also variation from firing to firing, location on the kiln shelf, and it goes on and on. If you cap a simple coating like CBS boxes or circles, the coating will go dark. If you don't cap it, you will retain most of the color, depending on how hot you go. If you don't cap the premium colors, some or them will popcorn, especially the really pretty ones (not the blue ones). If you look on the CBS website, you will not see anything about which coatings don't do well with a clear cap and which are more prone to "pop-corning". Finally, if you use etched dichroic from a company like Profusion which primarily uses CBS, you will learn about dark results and popcorn, but with the added premium of the very expensive etching.
Unfortunately for me, the unexpected results are what makes the process interesting. If I got exactly the same result every single time, I would have probably quit a long time ago. These same unpredictable results contribute to frustration and people moving to another craft.
