I don't usually bother with changing villagers' outfits at all in VV4. In VV2 and VV3 I'd change the doctors' clothes to white, so that they could be more easily spotted, but in VV4 we try to train every villager in every skill so in a way one villager is as good as another for healing.

The only times I have changed peeps' clothes were shortly after I got the game, and I wanted to see what was available, and some female villagers who have a rather unattractive mud-brown dress, which looks particularly bad with some hair colours. I've only done it late on in the game, though, when there's little or nothing else left on which to spend tech points anyway.