You may not layer translucent colors or use blending (even for lighting etc.).
Only the 8 colors can be displayed while the game runs.
This means that you must be careful with lighting because of shades. Those shades should still be displayed as one of the palette colors. If we'd be to screenshot the game at any given time, each pixel should be exactly one of the 8 colors of the palette.
Setting V value would give another color. Outline color must still be a color from the palette.