Today (Singapore time) is the 20th Anniversary of Pokemon! With this year's celebration's theme being "Train On", I decided to do an illustration centered around the various trainer types you faced in Kanto.
One of the difficulties when creating a multi-figure illustration, besides composing the image, is choosing colors. With characters and creatures that run almost the entire spectrum of the color wheel, it's very easy to run into what I call the "Megazord" effect.
The Megazord is a combination of all the individual Power Rangers robots. And because of that, the colors on this robot contrasts directly with one another. It is very difficult to place such an object into a scene and make it seem believable. If you wanted to paint the robot and tried to color pick from the above image and use it directly, it can lead to very disastrous results. Unless it's the style you're going for, it is generally unwise to paint with pure hues. Color is relative, and if you examine a photograph, what appears "Red" may actually be a dark shade of Orange in isolation. How then, can you pick the correct color that fits into the scene you're creating? One of the simplest solution is to identify the light temperature within the scene.
Every color has a warm and cool tone. Take Red for example:
The Dark Orange on the left is the warm tone while the Deep, almost Dark Pink, Red is a cooler tone. They both read as "Red" when place in the right context, but gives a different description to the lighting within the scene.
The above is the same Megazord robot in the TV show. The cool lighting unifies the contrasting colors and grounds the figure in the scene, making it much more believable than the toy photo from above.
Here are some more links to reading materials regarding this subject. They're probably better worded than my blog entry, but I hope it better informs your color choices in the future.