"My egg is yellow."
Translation:Mit æg er gult.
Because "Mit æg" is singular. Only attributive adjectives are inflected based on both gender, number and definiteness. Predicate adjectives only agree with gender and number.
If the adjective in this sentence were attributive, it would have been "gule":
- My yellow egg => Mit gule æg ("gule" is the definite singular neuter form of "gul")
But because it is used as the predicate of the sentence, it agrees only with the gender (neuter) and number (singular) of "æg":
- My egg is yellow => Mit æg er gult ("gult" is the indefinite singular neuter form of "gul")
If the sentence had been plural ("My eggs are yellow"), the Danish sentence would have been: "Mine æg er gule". Here, "gule" is the indefinite plural inflection of "gul".