For this Poster I put an extra hue of blue over the whole poster and chose the layer type 'color'.  The colors are together in the color wheel triangle so they work together.

Colour Wheel

A colour wheel is an  organization of color hues in a circle, that shows how primary colours, secondary colours and tertiary colours are related.

The kinds of colours:

Primary Colors: Red, Yellow, Blue. These 3 colors are the base colors for every other color on the color wheel. This is why they're called "primary." When you mix two primary colours together, you get a secondary colour.

Secondary Colors: Orange, Green, Purple. These 3 colours are what you get when you mix the primary colors together. They're between the primary colors to show what colors they're made from. Ex: Green is in-between yellow and blue. Green is made from blue and yellow.

Tertiary Colors: These are the colours that are made from one secondary and primary colour, like Red-Orange and Blue-Violet. There can be endless combinations of tertiary colors, but this depends on how you mix them.

RULES

Rule of Thirds: power shown from left to right, top to bottom. Use the grid, intersections.

Rule of Hierarchies: Objects and people above or in front have greater power and importance.
Rule of contrast: Use of darkness and brightness to emphasize objects, create mystery, sense of uncertainty, suspense.
Rule of Repetition: For emphasis and reinforcement but KISS (Keep it simple stupid/silly).

Rule of Alignment: Things are aligned with one another. No widows or orphans.
Rule of Proximity: Things are equal distances from one another, and the edges of the document.