****this is not, strictly, a java question, but I need a straight answer...
When making a sprite in adobe ImageReady I go *NEW
and it asks if I want to do "transparent", "background",
Now for a sprite, I use transparent and for a map tile I use background?
Well, I''m personally using Paint Shop Pro, but I''d say yes. You want Transparent for any sprite images.
For Tiles, it''s a toss-up. For base tiles (assuming you are doing a simple 2D tile engine and not Iso-Hex) either background or white will be fine (as you will be covering the whole surface anyway). For Some tiles (Object tiles for instance...think StarCraft), they will need to be Transparent.
If you are doing an Isometric or Hex engine, Transparent is the way to go for all.