Q: Is it OK for an adjective to modify another adjective? And if so¸ what is such a combination called?
A: An adjective modified by another word (whether hyphenated or not) is often called a compound adjective.
Usually a compound adjective consists of an adjective plus an adverb (as in “seemingly impossible task” or “apparently perfect crime”).
But it can also consist of an adjective plus another adjective. Examples: “near-fascist organization” … “bright red dress” … “icy-cold hands” … “golden-brown skin” … “bitter-sweet flavor” … “red-hot pincers.”
Many compound adjectives involving numbers, like “two-hour delay” or “eight-pound baby,” are examples of adjectives modifying adjectives. (The nouns “hour” and “pound” here are functioning as adjectives.)
In his Essentials of English Grammar, Otto Jespersen refers to adjectives that modify other adjectives as tertiary adjectives (pages 88-89).
If this hasn’t satisfied your interest in compounds, see The Cambridge Grammar of the English Language, pages 470, 1657-58.