As an illustrator, I think it is important to use bright colours in your work, so I always spend a lot of money on brush pens of various colours.
There are three reasons for that:
1. Using primary colours gives your work an edge.
2. If your work is cartoon-like or suited for children's books, bright colours are the way to go, and are sure to impress future clients when they look at your work.
3. Red, green, blue, yellow, pink and amber can present your character in a positive light, compared to grey brown or black. Dark colours dim the picture.
So, next time you are drawing, make sure you invest in some quality brush pens, and soon enough you'll have created some masterpieces.