There’s been a lot of debate, and my content is mainly conjecture based on of experience (and what has worked for me, at least in my head), but many solid arguments have been made, so here’s a translated excerpt from a post from the Japanese Language Center here to provide input from a native speaker. If anyone finds any issues with my interpretation, please do elaborate. I’ll be starting from point 2, as the beginning content is anecdotal and ひと is fairly straightforward.
“When a word expressing the actions (behaviors, movements; see 動作) of a person precedes 人, it is said as 「にん」.”
Several examples are listed, but the scheme seems to be that most nouns capable of being する verbs or that conjugate directly into a verb using kun’yomi result in the 「にん」reading.
"When a word describing the attributes or condition (status, state; see 状態 of a person precedes 人, it is said as 「じん」.
Examples include nationality (日本人) and adjectives (美人 from 美しい人 and 老人 from 老い人。
The writer also emphasizes that there are exceptions, but states that having general idea where to start is better than simply trying to memorize every instance of the kanji.
I can screenshot it after work. I’ll likely edit it into this post. Pretty sure it’s 飴色, but I’d hate if I not only misunderstood but also missed a potential kanji to learn.