Colours can be vibrant and vivid or they can be dull and uninspiring. Strong colours can jump out at us at times and create a positive sense of surprise or even amazement, while others, depending on where they appear and how they are presented, can null our senses and create no impression at all. Warm colours, for example, (in this case, typically yellow, orange and red I reckon) can brighten up a person's home and make it a more attractive place for guests to want to spend time. It should come as no surprise, therefore, that expressions describing emotions, personality times or specific circumstances are very often linked to colours. If any worldly phenomenon is universal to human language, it must surely be the incorporation of idiomatic references to colours into our daily speech.
Equally unsurprising is that in English (as, I presume, in most languages) warm colours tend to be associated with strong feelings or emotions. Cool colours tend to be more associated with neutral or perhaps even negative sensations or phenomena. Let's delve into this a bit more and look at some examples.
Red, because of its bright, striking nature, is definitely a colour that is associated with passion: be this of a positive or negative nature. If one sees red, one suddenly feels angry about something. However, as we all know from the colour coding of traffic lights (red signifying "stop") it is also a colour that represents danger or the concept of issuing a warning. If a company's finances are described as being in the red, this means that they decreasing and are at risk of deteriorating even further.
Pink may also be described as a warm colour. It is one that is often associated with mirth and cheerfulness. It can also bear the connotation of good health. Take this sentence as an example: "A year after recovering from cancer, Mr Smith was back in the pink of health." Since many Caucasian people have a slightly ruddy/pinkish facial complexion, the phrase is perhaps suggestive of the healthy returning of colour to an individual's face after a period of illness, during which their face colour may have turned paler than usual.
Green is said to be one of the most soothing colours. It is associated with the environment and thus with cleanliness. However, in human terms, it can also be linked to feelings of jealousy (green being an unnatural colour in terms of human pigmentation). Someone who is experiencing an immense sensation of jealousy due to something someone else has acquired (be it romantic love or monetary gain), and which they find themselves unable to obtain, is said to be green with envy.
Undoubtedly the dullest colour known to man is the colour grey. There is nothing many tourists loathe to see more on their holidays than grey skies! However, what is dull is often also associated with the concept of being vague and open to interpretation, perhaps because the two are reminiscent to many people of certain dry, overly lengthy legal documents that leave that leave the individual feeling baffled and unsure of what they have just read at the end of it! Maybe the colour grey is associated both with dullness and a lack of clarity because of the way in which grey clouds block light coming from the sun and the fact that they prevent us from seeing the sun itself. Here is a sample sentence that illustrates how the word grey can be used in the context of describing ambiguity ("grey area" being a common phrase and collocation used in English): "The issue of defining where exactly the line between the protection of free speech and the preventing of hate speech lies has always been a grey area."
To finish off, here's an expression whose connotation will probably not come as a surprise to you: as good as gold. Gold, being such a precious metal, is associated with all things prosperous and fortunate. Perhaps, however, you weren't aware that this phrase frequently refers to a person who is described by someone else as being particularly kind or pleasant. In fact, it is often used in reference to well-behaved, compliant children who cause no problems for grown-ups! If you happen to engage in babysitting from time to time or know someone who does, you or your friend might say to the parents of the child being looked after when they return home: "Little Johnny didn't cause me an ounce of bother,* he was as good as gold!"
*Colloquial expression meaning "no trouble"