My monitor is calibrated more for print, so I find the black text on the white background is great for me. The black text on blue comes second. The white text on blue places more emphasis on the box than the text, and the text looks a little washed out.
Since there is a difference in what they mean, I think the balloon and the Clipboard should be different. I prefer the black on blue balloon and the white clipboard.
I like black text on blue balloon and black text on white clipboard or maybe black text on yellow clipboard. White on blue is nice combo but is more difficult to read for me --especially if there is more text to read than what is in the examples---- like there will be I am sure...
One complaint I have with these things is that the author does not leave enough time to really read everything before the arrow is off to the next move. Some tuts have the click next to proceed/pause which solves this problem---whichever it is I hope enough time is given.Sometimes the fact that there is a pause feature is not so evident...
there is also the scenario where someone "thinks" they can speak English and will need time to really digest what is being said in the balloon /clipboard. Normally they can do well with the language, but maybe not in this sort of case...