Attention is selective, and often unconscious.*
The brain is always trying to make patterns in information in order to process it more effectively.
A consistent use of colour to relate connected information is a simple and effective way to help your users make your content easier to process.
But the colour doesn't have to be obviously related to a particular thing so that that new users get it on their first visit. Instead they learn the pattern the more they interact with the content.
It doesn't necessarily even mean that you can ask a user afterwards, what colour they think is associated with something - chances are they won't be able to tell you. But subconsciously the brain builds a pattern and helps them filter information based on colour. Similar to hearing your name mentioned, cutting through all the background noise at a party.
The key is consistency - avoiding overuse of colour and avoid conflicting or misuse of the colours. Cross channel usage is also important: desktop, mobile, tv, retail, etc. It's also important to assign colours to topics users may be familiar with through other channels. Yellow for sport would be wise, and green for ecology and environment for example.
Icons work more consciously, but colour runs much deeper.
* ref: 100 things every designer needs to know about people, by Susan Weinschenk