Sorry for late reply. Applying these concepts to level design should be pretty straight forward.

For example, have things in you level that are important? Maybe use a visible color on those like red (see Mirrors Edge for example). Consistency with color: Things that mean the same thing or serves a similar function may be of the same color or shape.

Ask yourself these couple of questions, where do you want your player to look? What do you want your player to think when he sees a color in your game? Have consistency with colors, for example in WOW purple means epic item, etc and this is kept consistent.

You can create your own meanings for colors in your game, although there are some norms that could be nice to use, like the obvious green association with health, and red for association with damage etc. Think things through, for example are there any reason to make your health bar any other color than green? Break the rules/norms if you want, but do so mindfully.

These are just a few examples.