The Gen1 evolution animation still has color images. @Vendea tried a few different things to get the images greyscaled, but they unsuccessful.
One possible solution, not yet tried, would be to modify the 64-bit dataURL which is stored as a character string in the Image class instances. Given a color image "squid", this should be possible with code like:
var newDataURL = squid.src;
// iterate across the character string as appropriate
var bwSquid = Image(newDataURL);