Why is 色んな an adjectival and not an adjective? I encountered the word here: ! and the 'adjectival' definition in < * * * * * * **Edit:** Both @Leebo 's and @Aeon Akechi 's answers did answer my question and were rich of useful information. But I accepted the longest answer.

It cannot be used as a predicate. It can only come before a noun to directly modify it, the way that it modifies in the sentence you provided.

So you cannot end a sentence with things like

>
>

Things that are described as adjectives can of course directly modify a word, but they can also be used as a predicate. For instance, the related word is a adjective.

So you can say or you can say