Theming App

Ionic is built on top of Sass, which allows you to set some default styles for your app but makes it extremely easy for you to change defaults.

just tweak the :root map in your src/theme/variables.scss

:root {
  /** primary **/
  --ion-color-primary: #075e54;
  --ion-color-primary-rgb: 7,94,84;
  --ion-color-primary-contrast: #ffffff;
  --ion-color-primary-contrast-rgb: 255,255,255;
  --ion-color-primary-shade: #06534a;
  --ion-color-primary-tint: #206e65;

  /** secondary **/
  --ion-color-secondary: #0cd1e8;
  --ion-color-secondary-rgb: 12, 209, 232;
  --ion-color-secondary-contrast: #ffffff;
  --ion-color-secondary-contrast-rgb: 255, 255, 255;
  --ion-color-secondary-shade: #0bb8cc;
  --ion-color-secondary-tint: #24d6ea;

  /** tertiary **/
  --ion-color-tertiary: #21ba5a;
  --ion-color-tertiary-rgb: 33,186,90;
  --ion-color-tertiary-contrast: #ffffff;
  --ion-color-tertiary-contrast-rgb: 0,0,0;
  --ion-color-tertiary-shade: #1da44f;
  --ion-color-tertiary-tint: #37c16b;

  /** success **/
  --ion-color-success: #10dc60;
  --ion-color-success-rgb: 16, 220, 96;
  --ion-color-success-contrast: #ffffff;
  --ion-color-success-contrast-rgb: 255, 255, 255;
  --ion-color-success-shade: #0ec254;
  --ion-color-success-tint: #28e070;

  /** warning **/
  --ion-color-warning: #ffce00;
  --ion-color-warning-rgb: 255, 206, 0;
  --ion-color-warning-contrast: #ffffff;
  --ion-color-warning-contrast-rgb: 255, 255, 255;
  --ion-color-warning-shade: #e0b500;
  --ion-color-warning-tint: #ffd31a;

  /** danger **/
  --ion-color-danger: #f04141;
  --ion-color-danger-rgb: 245, 61, 61;
  --ion-color-danger-contrast: #ffffff;
  --ion-color-danger-contrast-rgb: 255, 255, 255;
  --ion-color-danger-shade: #d33939;
  --ion-color-danger-tint: #f25454;

  /** dark **/
  --ion-color-dark: #222428;
  --ion-color-dark-rgb: 34, 34, 34;
  --ion-color-dark-contrast: #ffffff;
  --ion-color-dark-contrast-rgb: 255, 255, 255;
  --ion-color-dark-shade: #1e2023;
  --ion-color-dark-tint: #383a3e;

  /** medium **/
  --ion-color-medium: #989aa2;
  --ion-color-medium-rgb: 152, 154, 162;
  --ion-color-medium-contrast: #ffffff;
  --ion-color-medium-contrast-rgb: 255, 255, 255;
  --ion-color-medium-shade: #86888f;
  --ion-color-medium-tint: #a2a4ab;

  /** light **/
  --ion-color-light: #f4f5f8;
  --ion-color-light-rgb: 244, 244, 244;
  --ion-color-light-contrast: #000000;
  --ion-color-light-contrast-rgb: 0, 0, 0;
  --ion-color-light-shade: #d7d8da;
  --ion-color-light-tint: #f5f6f9;
}

You Can generate these colors by using ionic color generator.
its in beta stage but believe me its superb

https://beta.ionicframework.com/docs/theming/color-generator