In the sentence Ez a szín csúnya., the adjective csúnya is used as a predicate adjective. How can we determine that? From the relative placement of the adjective to the noun (subject). If an adjective comes right in front of a noun (subject), i.e. between the article/determinative and the noun (subject), it is used as an attributive adjective. If it comes after the noun (subject) or before the article/determinative, it is used as a predicative adjective.
So, the parts are:
*van (implied verb) => is
csúnya (adjective) => ugly
szín (noun) => color
ez (determinative) => this
a (definite article) => the
If you want to translate this structure into English, you will have to uphold the predicative usage of the adjective. To accomplish this objective, you have to separate subject and predicate parts.
this + the + color => this color
ugly + is => is ugly, ugly is
This leaves us with the result:
This color is ugly.