Resource File, Image List and TreeView

I'm loading an imagelist for a treeview from a resource file, which works
fine for 16-color bitmaps, but 256-color look really bad (it appears they're
being converted to 16-color bitmaps).   If I load these 256 color images
into the imagelist at design time using the ImageList editor, the treeview
displays them just fine!

I appreciate any ideas.