Car or train or bus to see Pueblos Blancos

You can train or bus from seville to granada, both are good options and quite comfortable.
A question is how many white villages do you want to see? Or, the real question is "how many more white villages will you want to visit after seeing one?"
White villages look charming from a distance, but often lack any real attraction which creates a desire to visit more than one. I am speaking from personal experience and the opinions voiced by others from a variety of sources. There are a couple of RS contributors whom I hope see your post (ed and brad) whom have a lot of experience with this travel.
Meanwhile, we love Andalusia and always rent a car to travel-but...... We are history and architecture nuts whom find small nuggets of interest in the tiniest of places.

There are hundreds of towns and villages which could count as white villages. Whilst bus touches almost everywhere and train a few, you are only going to be able to link at most three or four together in one day by public transport and almost certainly not at times to suit you. I would not say there are a great many in the vicinity of Granada and you ought to be visiting after Seville or between the two.

Many of these villages are attractive from afar, attractive within and maybe have one other attraction which might occupy for an hour. Google Pueblos Blancos, see what attracts you.

And what about the former white village which is now painted blue?

Rick only suggests Zahara and Grazalema for people traveling by car; Arcos and Ronda are fine by bus and train if you work around their schedules. A couple of direct buses per day run from Sevilla to Arcos, or more buses with a connection at Jerez. Or, you can easily get from Sevilla to Ronda by bus or train. On p. 774-5 of Rick's Spain book, see notes about checking bus schedules carefully, as posted info is not always up to date.