Kangaroo Mode

(From the 7800 Software Guide:)

Bit 2 ($04) of CTRL enables "Kangaroo" mode which eliminates transparency, so that any pixel of color "0" will be background color, rather than transparent.

Most games will leave this off since it would result in rectangular sprites. 

However, the 7800 Software Guide also mentions Kangaroo mode in relation to the 320 modes. The 320 modes have a quirk where transparency only works if the even/odd pair of 320 pixels are both color "0". Otherwise any pixel of color "0" will be background color, rather than transparent.

Although Kangaroo Mode should only impact overlapping sprites, there appears to be some impact on 320B & D modes as well.  Attached is a simple test program which displays all 6 graphics modes onscreen. Press player 1 button to enable kangaroo mode, press player 2 button for colorkill (may be combined). (CC2 7800_8K 78QUICK, should work on both NTSC and PAL)

Okay, what are you looking at, eh? The screen is divided into 9 areas (3x3 grid):

320A (palette 0-3) 320C (palette 0,5,6,3) 320A (palette 4-7)

320D (palette 0-3) 320B (palette 0,5,6,3) 320D (palette 4-7)

160A (palette 0-3) 160B (palette 0,5,6,3) 160A (palette 4-7)

And for each palette byte values 0-255 in a 16x16 grid (see the code for the palette values).