Applying Colors to Materials:
When colors are applied to these materials and "Tint Surface" is checked, they are multiplied to the color - so colors will be darkened if the material is dark. Use whiter materials if you need to apply a color that is a close match to the color being applied.

Shadows, etc:
Just like in real life colors will be effected by the lighting in a scene. Use the F key to apply color to the view in front of you. To turn up the brightness of the light, press the A key and to see the spotlight, right-click it and turn up brightness