We should avoid white sugar or so called "brown sugar" which is basically refined white sugar with molasses added to it. What we should purchase is natural brown sugar. At the supermarket look out for the following brands: demerara sugar (common in uk) or turbinado sugar (common in the us)
I believe only naturaly brown sugar is acceptable for degh.
ref: [
en.wikipedia.org]
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥