Is it possible for an adjective to modify another adjective?

Let's say the noun Joe wants to describe is the paper he just wrote. It has more pages than the average, so one adjective is long. We want to modify the way "long" describes the "paper", so we look for some words to make the modification.

Do we want an adjective? No, because "long" is not a noun, though it can be made a noun when you change it to "length". Rather, it is doing something to the word "paper" by describing it, so if we want to modify the description, we need to add an adverb.

For example, if we want to clarify that it is not necessarily among all papers that Joe's is regarded long, but only among this topic, then we might say "Joe wrote a relatively long paper".

an immaculate black three-piece suit

The absence of punctuation marks this as the 'stacking' of modifiers. Here there are two layers of modification: "three-piece suit" is first modified by "black" to form the nominal "black three-piece suit", and this in turn is modified by "immaculate" to give the interpretation "three-piece suit that is immaculate by the standards applicable to black ones".

By contrast, if a comma is inserted to give

an immaculate, black three-piece suit

then things are somewhat different. Here, "three-piece suit" is modified by a coordination of adjectives, giving the meaning "three-piece suit that is both immaculate and black".

Note: for clarity, I've ignored the compound adjective "three-piece", which is also a modifier.

An adjective doesn't modify another adjective. In the case of the

immaculate black three-piece suit

"Immaculate" can only modify the noun "suit".

In the case of

bright red car

There are two ways to parse this. The first is that "bright" modifies the noun "car" directly. The car is both red and bright.

The second (and more usual) way to parse this is to treat "bright red" as one single modifier. The noun is modified by one colour adjective, and that color is "bright red"

Neither of these involve an adjective modifying an adjective.

The reason why we have color terms like "bright red" is because color terms like "red" can take the grammatical role of a noun ("use red with green to make a Christmas theme"), and therefore we can modify them with adjectives. Then we can take the result and use the compound whole as an adjective.