Degree modifiers are words like 'very', 'barely', and 'almost'. Spem degree modifiers fall into two categories:
Ones that describe a trait with no clear line between meeting or not meeting criteria. Examples of adjectives usually used this way: tall, hot, fast. Modifiers used this way: slightly, mediumly, very.
Ones that describe traits that are relatively binary or that have a binary threshold from context. Examples: finished, ready, open. Modifiers used this way: almost, barely, completely.
Note that adjectives are not inherently bound to only one of these categories. Most if not all adjectives can be used either way depending on context. For example, if you're sorting objects into two groups based on height, "tall" could be used in the second way.
"Green" is an adjective that's natural both ways, even without extra context. "Slightly green" means something has a green tint but not enough to be called green; it's more something than else than green. "Barely green" means it's green enough that you would call it green sooner than another color. "Very green", depending on context, could mean much more than either slightly or barely.