Can't happen, most likely it seeded and the new plant is white.
Linda C

Some flowers do indeed change colors based on growing conditions, but whether this can happen to dianthus I haven't a clue.

I am having a similar issue, if anyone in 2022 has an answer, that would be wonderful...My dianthus use to be this beautiful pastel light pink, but now its this generic deep bright magenta/hot pink color. I don't like it at all...something makes me feel as though its something to do with the soil. But a legitimate answer would be wonderful..

Thank you so much for this response! @gardengal48 (PNW Z8/9) is there anyway to undo the reversion?

Sorry, no. You will need to replant with the color you want. And then not allow it to self seed :-)

It is also fair to say that some seedlings could very well bloom in the original color as well.

Aw man that is a bummer...at least I now know its definitely not the soil.

thank you for all this info, time for me to head out to the nursery lol!

There appear to be some dianthus that do change color with age of the blooms How Flowers Change Colour | Mr Plant Geek

Temperature can significantly change color of flowers in some plants. For example, here's the blooms on my miltoniopsis orchid right now, the darkest ones bloomed while temps were cool and the lightest when it was warm/hot.

The pale pink Dianthus reverting to the parental genetic norm over a period of years is just reversion, not soil, temperature or bloom age.

is the reversion inevitable over time?? I have a broad slope of pale pink, almost white, dianthus that would be ghastly if it were magenta..

If you can keep deadheading and remove all seedlings...

Besides, not all pale pink dianthus would have hot pink ancestry. So, your pale pink may revert to something other than hot pink.