Sounds like they're goners - if the white is fuzzy, like a deposit, then sounds like damping off or similar, if you mean the plant tissue is actually white, that'll be cold temperatures.

If a cutting changes colour you can be virtually certain you've lost it.

Best to try again

Bin them and start again. This time of year your best chance is using bottom heat in a propagator. I find non-flowering cuttings in August seem to be the most successful.

Wiuth dwarf dianthus I find thery divide quite easily . Just pull them apart with several stems to a clump.

Last year I put together a sequence of photos showinh how to propagate dwarf dianthus

Here it is

http://www.flickr.com/photos/31559373@N00/5822263112/in/photostream

I don't want them at all - can't stand the things in the garden, other than the dwarf forms of Dianthus...

I'm with you on that Bamboo. The longer stemmed dianthus have lovely flowers but they're so lax in habit I don't like them.

Some of the dwarf dianthus are as attractive ,have almost as lovely a scent and have a much better growth habit

Not so good for cut flowers though.

....................... unless you're using a very tiny vase

Ha ha, yea, a thimble...