One of my past students Nancy Choi, sent me a project she finished a couple months ago.
This is a room used for art class for kids from grade 1-6 at her Pastor's drop-in center. The colours she used are as follows: Carrie Bradshaw's electric blue, yellow highlighter, stem green and purple hyacinth, from Benjamin Moore.
Colours by Nancy Choi
The colours had to be strong enough to create contrast against the stark white walls and the words spelled inside the circles so they could be seen, as well as clean and bright enough to highlight the element of fun and play that she created using polka dots. I think she did a great job!
Colour, fundamentally, can only be described in three ways, it's either Light or Dark, Clean or Dirty, Cool or Warm, period. And it's the clean/dirty shift that causes the most disharmony in a space, it mostly doesn't work which is what I also teach my students.
One of my other students was recently in a paint store (which shall remain nameless) working on a class assignment. She was talking to the in-store colour consultant about mixing clean (synthetic, bright colour) with dirty (muted or neutral) colours. This consultant said "You can mix clean and dirty colours, I do it all the time!"
So the following week she was back in class armed with this new evidence. My response was still the same, "You can do whatever you want when you leave this class, but at least you will KNOW when you are doing it because your eye will be trained."
There are not that many hard and fast rules in colour and design but there are guidelines. Once you know the guidelines, you can use your intuition and be creative, but not knowing them could be trouble!
The biggest challenge people have with colour in their home is in creating flow and usually if a colour consultant is not hired to pick colours, people end up either with very pale colours or they just pick a colour and go from varying shades of light to dark (using one colour) throughout the house.
A space that feels harmonious when you walk in, most likely has a palette of varying shades of neutral tones or cleaner, fresher colours if that's what the decor dictates.