They have now used the Ubuntu installation. After changing all the colors (their very first comment, without any prompting, was that the colors and desktop were incredibly ugly) they are tentatively accepting it.

So do you have anything new to add other than the fact that people have subjective tastes? I do not mind the colour and nor do the others who I've installed it for. Indeed I would guess that you subtle hints and negative behaviour most probably caused them to react that way.

And in any case, that's a ridiculous thing to raise when you have nothing more to rant about. Obviously it is not forced upon you and you can change it within seconds of logging in.