Lamb icons, fortresses with the same icon background as lamb dominants, cross icons (heroes), Bible icons (good enhancements), covenants (Bible and artifact icons) are all considered good.
Grim Reaper icons, fortresses with dark multicolor icons, dragon icons (evil characters), skull icons (evil enhancements), curses (skull and snake icons) are all considered evil.
Lost Souls, sites, artifacts, are all considered neutral.
For deck building purposes (mostly T2) DAEs (enhancements with both Bible and skull icons) are technically considered half good and half evil and can be targeted as either in the deck. In type two, since they are half good and half evil they are effectively neutral and are counted as such.
Technically, yes. Any card with more than one brigade are considered multicolor but usually are referred to as two-color, tri-color, and now quad.