Intensity means how clear or bright the color is. What can be confusing is that pastels (light values of colors) can also be bright. Hot pink may be pink, but its certainly vivid. There are no right or no wrong color or value mixes.
But when you choose colors of the same value and intensity, the effect is naturally harmonious. If you want your overall effect to be light and airy, without the drama of sharp contrast, choose equally pale shades of the dominant colors you are using. DINING TABLE DESIGN SIZE
Pair a pale shell pink, for example, with a delicate apple green rather than a jewel tone forest green.
Or, if you lean to brights, plan your main scheme so the colors balance each other. In the bedroom, above right, the buttery yellow is intense and bright enough to visually hold its own with the deep, vibrant red. Repeat colors, shown in the mix of fabric patterns, tie two strong hues together.
Left: Pretty pale schemes work because tints of delicate color amplify rather than compete with each other.