"Mae'r ffrog wen yn iawn."

Translation: The white dress is OK.

[EinarSig]

I thought white was 'gwyn'?

[EllisVaughan]

In Welsh certain adjectives come in masculine and feminine forms. White=Gwyn(m)=Gwen(F). "Gwen" then mutates to "wen" because it always follows a feminine noun, So "Y Ffrog wen" because "ffrog" is feminine.

[EinarSig]

Ah okay, thank you very much!
Have a lingot!