[neilep (OP)]

Doesn't matter what colour the soap bar is...why are the soap bubbles white ?...or aren't they ?



Men are the same as women, just inside out !

[daveshorts]

What white means is that all the colours of the rainbow are bouncing off the stuff in random directions. The reason that foam looks white is that the light is reflected and refracted off lots of surfaces, so it ends up coming out in pretty random directions.

If you think of how much of a bar of soap you use per bubble the amount of colourant is minute, so the relections and refrations which do not care what the colour is dominate. if you looked through 1000 flat soap films (that were thick enough for interference not to be an issue) then they may start to look like the original colour.

The colours you can see in a single film are due to reflections from both sides of the film interfering and sending some colours straight through and reflecting others. Because it is just splitting the colours rather than absorbing some, when you have a foam and there have been lots and lots of reflections everything pretty much cancels out to white again.

[Karen W.]

Hummmm, I never paid any attention to that before, I wonder why?........... Yep your right, even my big pink beauty bar does not make pink bubbles!

Karen

[eric l]

Well, if you could make foams of similar structure from differently coloured soap bars, and observe them at the same time and with ideal light conditions, you may see a difference if you are a trained observer.  But that's a lot of conditions.
Using an instrument for evaluating the colour of reflected light probably will show a difference, too.
Compare it to this :  if you prepare a sugar solution at 1.33 % and an other at 1.35 %, a good refractometer or polarimeter will show you the difference.  But unless you are a trained observer in that field, and regularly participate in tasting panels, you'll never taste the difference.

[realmswalker]

http://www.zubbles.com/
go check that