Flutter uses Flutter Material Colors Class and Flutter Dart-UI Color Class to paint colors on your app screen. 

  • Flutter Material - Colors Class
  • Flutter Dart-UI - Color Class
Flutter Colors Demo
Flutter Colors Demo

How to apply colors to my flutter app ? 

How to use Flutter Material Colors Class ?

Flutter Material Colors Class - Documentation

Also refer official class documentation with this guide to deeply understand the concept.

Let us start with the simplest way to apply colors to your flutter app widgets.

1. Colors class - Use Color using COLOR NAME (class constants) 

color : Colors.orange

Colors Class Constants
Colors Class Constants
Orange Container Widget UI
Orange Container Widget UI

2.Colors class - Use Color using COLOR NAME & COLOR SHADE

  • Color shade ranges from 100 to 900 in increment of one hundred
  • Color with shade 50 is also added to above range in some colors
  • Accent Colors have only shade values 100,200,400 and 700
  • Lower Shade Value - Pale Color
  • Higher Shade Value - Darker Color
Darker Orange Shade - Colors.orange[900]
Darker Orange Shade - Colors.orange[900]

How to use color shade value ?

  • Colors.orange[900]
  • Colors.orange.shade900

Both of the above methods have same output

Colors.orange[900]
Colors.orange[900]
Colors.orange.shade900
Colors.orange.shade900

Both the above methods have same output 

Color Shade Orange 900 UI
Color Shade Orange 900 UI

Note :  Colors.orange is same as Colors.orange[500] or Colors.orange.shade500

3. Colors class - Black and White Colors

  • We have separate set of constants for color black and color white
  • These colors are identified by their transparency and not shade values.

Example 

  • Colors.black54 - pure black with 54 % opacity
  • Colors.black12 - pure black with 12 % opacity

  • Lower Number - Transparent Color
  • Higher Number - Opaque Color
White & Black Colors
White & Black Colors

Note : Transparent Color - Colors.transparent constant - entirely invisble

How to use Flutter Dart-UI Color Class ?

Flutter Dart-UI - Color Class - Documentation

Also refer official class documentation with this guide to deeply understand the concept.

Let us first understand the basics of colors.

Color channels

  1. Red Channel 
  2. Green Channel
  3. Blue Channel
  4. Alpha Channel (Transparency)

Color Class Properties

  • Alpha Property - Docs

    • Alpha Channel of this Color is in 8 bit value
    • 8 bit value mean range 0 to 255 (2 raise to 8 = 256)
    • 0 means this color is fully transparent
    • 255 means this color is fully opaque
    • return type int

Alpha Property Summary

8 bit value  - 0 (transparent) to 255 (opaque)

  • Opacity Property - Docs

    • Alpha channel of this color is in double value
    • double value mean ranges from 0.0 to 1.0 
    • 0.0 means this color is fully transparent
    • 1.0 means this color is fully opaque
    • return type double

Opacity Property Summary

double value - 0.0 (transparent) to 1.0 (opaque)

  • Value Property

Color represented as 32  bit value

Bits are assigned as follows :

  • Bits 0 to 7 Blue value (Blue Channel)
  • Bits 8 to 15 Green Value (Green Channel)
  • Bits 16 to 23 Red Value (Red Channel)
  • Bits 24 to 31 Alpha Value (Alpha Channel)

Difference between Alpha and Opacity

Alpha sets alpha channel value in 8 bit value and Opacity sets alpha channel value in double

Let us also understand what is 0xFFFFA726 ?

Orange Int Value
Orange Int Value

In the common “hash syntax” we represent color values as #FFA726 (Ignore 0xFF at the beginning).

color picker tool
color picker tool

Using a color picker tool, we get the same color ie. Colors.orange[400] using “hash syntax” #FFA726

If we convert hex code to decimal code, we can get the RGB values.

  • Red Channel FF (hex) equals 255 (decimal)
  • Green Channel A7 (hex) equals 167(decimal)
  • Blue Channel 26 (hex) equals  38(decimal)

Thus,  0xFFFFA726 is 0x FF(alpha) FF(red) A7(green) 26(blue)

Now, we have understood all the basics of color values and color channels we can now proceed with implementation code of the constructors of the Color class

Color Class Constructor

1. fromARGB Decimal (int) => Color.fromARGB(int a, int r, int g, int b)

color : Color.fromARGB (255,255,167,38) // fromARGB Decimal

ARGB int
ARGB int

2. fromARGB Hex 

Note : Add 0x to the value, for example, Green channel (hex) A7 will become 0xA7 

color : Color.fromARGB (0xFF,0xFF,0xA7,0x26) // fromARGB Hex

ARGB Hex
ARGB Hex

3. fromRGBO Decimal (int) => Color.fromRGBO(int r, int g, int b, double opacity)

color : Color.fromRGBO(255,167,38,1.0) // fromRGBO Decimal

  • O stands for opacity - refer above explained opacity property summary
  • double value - 0.0 (transparent) to 1.0 (opaque)
RGBO
RGBO

4. Color - Color(int value) - 0xAARRGGBB

  • Get any color int value for example #FFA726
  • Add 0xFF to “hash syntax” FFA726 => 0xFFFFA726
  • 0xFF added to hash syntax is the alpha channel FF(hex) => 255 (decimal) opaque color

color : Color(0xFFFFA726) // int value

Color Int Value
Color Int Value

Output UI Color for all above 4 constructor is same 

Color Constructor Output
Color Constructor Output

Coding - Sample Flutter App Code

To learn more about flutter - Flutter Developer Guide