Ah, monochrome: sometimes all you want a single hue in your life. Designing a room in one color can be challenging but also very fun. But a great way to avoid the disaster of mismatched robin’s egg blue is to create a room that embraces a singular color but peacocks out using different shades of the original tone.
I believe blue to be one of the most approachable colors for interior design. Not only does blue have a calming effect but it also has the ability to be gender neutral depending on the design with which the blue tone is paired. Blue velvet can be an eye-popping success when paired with other elements that balance out the brightness and boldness of colored velvet. Another great thing about blue is that, to me, it absorbs light really well: natural light just enhances the deep hues of this primary color and lamplight reflects the shade well too.
So, really, when in doubt, do the blue.