Comparing Four Deep Blues: Cobalt Blue, Ultramarine Blue, Dioxazine Purple and Prussian Blue

Deep blues and blue-violet colors play an important role in watercolor palettes.

They are frequently used for skies, water, shadows, landscapes, atmospheric perspective, and structural depth.

Compared with lighter blues, these colors often show greater color density, stronger visual weight, and more visible pigment texture.

This group includes Cobalt Blue, Ultramarine Blue, Dioxazine Purple, and Prussian Blue.

Although all four belong to the cool side of the color spectrum, they differ significantly in color temperature, granulation, transparency, and their relationship to blue, violet, and blue-green.

Together they create a transition from neutral deep blue through blue-violet into deep blue-green.

Comparing Four Deep Blues: Cobalt Blue, Ultramarine Blue, Dioxazine Purple and Prussian Blue

Cobalt Blue: A Classic Deep Blue

Cobalt Blue represents the most neutral blue within this group.

The color shows little shift toward either violet or green.

At full strength it produces a stable deep blue.

When diluted, characteristic granulation patterns become visible.

Pigment particles settle naturally into the texture of the paper, creating organic surface variation.

Suitable for:

  • Skies
  • Lakes
  • Distant landscapes
  • Shadow areas
  • Mountain structures
  • Natural textures

Comparing Four Deep Blues: Cobalt Blue, Ultramarine Blue, Dioxazine Purple and Prussian Blue

Ultramarine Blue: A Blue-Violet Classic

Ultramarine Blue occupies the position between Cobalt Blue and Dioxazine Purple.

Compared with Cobalt Blue, it contains a noticeably stronger violet component.

Granulation is pronounced and creates dynamic texture throughout washes and gradients.

The color is particularly useful for atmospheric subjects.

Suitable for:

  • Evening skies
  • Cloud shadows
  • Mountains
  • Seascapes
  • Atmospheric perspective
  • Night scenes

Comparing Four Deep Blues: Cobalt Blue, Ultramarine Blue, Dioxazine Purple and Prussian Blue

Dioxazine Purple: A Bridge Between Blue and Violet

Dioxazine Purple moves clearly toward the violet side of the spectrum.

Within this group it contains the strongest violet influence.

At full strength it produces deep blue-violet tones.

Diluted applications create transparent lavender and violet transitions.

Suitable for:

  • Night landscapes
  • Flowers
  • Deep shadows
  • Violet plants
  • Atmospheric backgrounds
  • Blue-violet transitions

Comparing Four Deep Blues: Cobalt Blue, Ultramarine Blue, Dioxazine Purple and Prussian Blue

Prussian Blue: A Deep Blue-Green

Prussian Blue occupies the position closest to blue-green.

It contains the strongest green component within this group.

At full strength the color can approach near-black blue values.

When diluted it reveals a cool blue-green character with considerable depth.

Suitable for:

  • Deep water
  • Ocean scenes
  • Forest shadows
  • Night subjects
  • Dark architecture
  • Storm skies

Comparing Four Deep Blues: Cobalt Blue, Ultramarine Blue, Dioxazine Purple and Prussian Blue

Color Relationships Within the Group

Although all four colors belong to the family of deep blues, they occupy different positions within the color system.

  • Cobalt Blue = neutral deep blue
  • Ultramarine Blue = blue-violet
  • Dioxazine Purple = violet-blue
  • Prussian Blue = blue-green

Together they expand the blue spectrum in two directions: violet and green.

Granulation and Pigment Character

One of the defining characteristics of this group is visible pigment texture.

Cobalt Blue, Ultramarine Blue, and Dioxazine Purple display noticeable granulation effects.

These characteristics create natural variation and texture across watercolor washes.

After drying, the colors develop matte surfaces while retaining their individual pigment structures.

Deep Blues Within a Color System

Deep blues form the foundation of many color mixtures.

Ultramarine Blue and Dioxazine Purple combine naturally with reds and magentas.

Prussian Blue produces rich greens when mixed with yellows.

Combined with orange, all four colors create strong complementary contrasts.

Together they connect blue, violet, and green color systems.

Half-Pan Format and Color Organization

All colors in this group are produced in half-pan format.

This format allows many colors to be organized within a compact palette while making comparisons between granulation, transparency, and color temperature easier.

Half pans are also suitable for long-term storage and portable watercolor palettes.

From Deep Blue to Blue-Violet and Blue-Green

From Cobalt Blue through Ultramarine Blue and Dioxazine Purple to Prussian Blue, different developmental directions within the blue family become visible.

Some colors move toward violet.

Others move toward green.

Together they form an important structural part of a complex watercolor palette.

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