A monochromatic color scheme uses variations of a single hue. Instead of combining blue with orange or green, you work exclusively with blues: dark navy for text, medium blue for CTAs, light blue for backgrounds, pale blue for hover states. It sounds limiting, but the constraint is the point.
Why Monochromatic Works
Harmony is guaranteed. Since every color shares the same hue, nothing clashes. The visual cohesion is automatic. This makes monochromatic schemes the safest choice for designers who are less confident with color and the most sophisticated choice for those who are.
Creating Variety Within One Hue
The key to a monochromatic scheme that does not feel flat is aggressive variation in saturation and lightness. You need very light tones (backgrounds), medium tones (borders, secondary elements), and very dark tones (text, headers). The wider your lightness range, the more dynamic the result.
The Neutral Backbone
Even monochromatic palettes need true neutrals. Pure whites and near-blacks provide the extreme contrast points. These are technically achromatic (no hue), but they complement any monochromatic scheme because they do not introduce competing hues.
Building in PaletteRx
Start with your single hue at full saturation, medium lightness. This is your Primary. Then add variations: reduce lightness for a dark variant (another Primary or Supporting), reduce saturation and increase lightness for a tint (Supporting), and add a near-white light base and near-black dark base. PaletteRx's balance scan will note low hue diversity, which is expected and intentional for monochromatic schemes.