When working with glass, the final product will often have a different color from when the glass was in its original state. The fired glass's color also depends on what type of base metal/glass is used. When making an enamel piece, blue glass powder won't look the same if it's placed on copper vs. silver or with a white vs. ecru enamel base. The same goes for dichroic glass.
Dichroic glass has even more surprises in store for the glass artist because dichros are multicolored to begin with. The glass has a prismatic effect and the colors shift as the light hits. The glass's hue also changes during the firing process -- sometimes even more than I'd anticipated.
With enamels, you have a pretty good idea how the color will turn out. Blue is almost always blue, though the final shade might be darker or lighter. Sometimes enamels will turn odd colors when fired on silver -- for instance, yellow becomes pink in this case -- but for the most part, you can predict what your piece will look like.
Well, dichroic glass continues to surprise me. You can shift the glass downward at a 45 degree angle to get an idea of how a fired dichro will appear, but this is not foolproof. This afternoon, I made two new pieces using some interesting patterned dichroic glass. On one piece, I used a black base and layered it with clear butterfly-print and pink mirrored glass. The end result? The clear glass came out dark blue, while the pink glass turned into shiny gold. I like it, but so weird!
I used a clear base for the second piece and fired that with some yellow dichro... and that turned out to be turquoise with deeper blue undertones. Not at all like the colors I chose.
This makes it difficult to repeat or design custom pieces since I can never be sure of how my glass will appear in the end. It's certainly an adventure working with it, though. I kind of like the fact that I can still be surprised.