ZomCoder wrote:
Is there ever any use for every fourth palette entry since they are treated as transparent?
No, they're always transparent. The only way they can be visible on screen is if you exploit the palette trick when the PPU is off. During normal rendering they will never be used.
EDIT - except for $3Fx0, which of course is used as the background color.
Quote:
Are these ever used as "codes" when doing sprite collision, etc.?
No.