Hi pals,
I just realized that the latest version sometimes showed a fifth colour!
This was merely a bug caused by clumsy coding. It wasn't my intention to cheat and I immediatly attached a fixed version which won't do this anymore.
You will most probably not notice any difference, but I thought I should clear this up.
How it happened:
For each pixel the dithering has to decide whether to use the current or next-brighter colour, so I just added a fifth colour to the palette (which is simply identical to the fourth colour) so I don't have to handle a palette-overflow or special-case.
I also toggle the palette for every frame, but on initialization I accidently copied the "overflow-colour" from the first palette to the end of the second palette. So in case of such an "overflow" the 2nd frame happened to show a fifth (and actually wrong) colour.
I'm sorry for this inconvenience.