Use colorScheme variable can custom your chart color. You can find description in doc.
https://swimlane.gitbook.io/ngx-charts/examples/pie-charts/pie-chart
custom colors for the chart. Used to override a color for a specific value
example pie chart
src/app.ts
//our root app component
import {Component, NgModule} from '@angular/core';
import {BrowserModule} from '@angular/platform-browser';
import {BrowserAnimationsModule} from '@angular/platform-browser-animations';
import {NgxChartsModule} from '@swimlane/ngx-charts';
import {single, multi} from '../data.ts';
@Component({
  selector: 'my-app',
  template: `
    <ngx-charts-pie-chart
      [view]="view"
      [scheme]="colorScheme"
      [results]="single"
      [legend]="showLegend"
      [explodeSlices]="explodeSlices"
      [labels]="showLabels"
      [doughnut]="doughnut"
      [gradient]="gradient"
      (select)="onSelect($event)">
    </ngx-charts-pie-chart>
  `
})
export class App {
  single: any[];
  // chart area size
  view: any[] = [700, 400];
  // options
  showLegend = false;
  showLabels = true;
  explodeSlices = false;
  doughnut = false;
  // your color scheme
  colorScheme = {
    domain: [
      '#FF8A80', 
      '#EA80FC',
      '#8C9EFF', 
      '#80D8FF', 
      '#A7FFEB', 
      '#CCFF90', 
      '#FFFF8D', 
      '#FF9E80'
    ]
  };
  constructor() {
    Object.assign(this, {single})   
  }
  // select event
  onSelect(event) {
    console.log(event);
  }
}
@NgModule({
  imports: [ BrowserModule, BrowserAnimationsModule, NgxChartsModule ],
  declarations: [ App ],
  bootstrap: [ App ]
})
export class AppModule {}
data.ts
export var single = [
  {
    "name": "Apple",
    "value": 8940000
  },
  {
    "name": "Banana",
    "value": 5000000
  },
  {
    "name": "Ornage",
    "value": 7200000
  },
  {
    "name": "Avocado",
    "value": 4830200
  },
  {
    "name": "Cherry",
    "value": 5520000
  },
  {
    "name": "Coconut",
    "value": 1200000
  },
  {
    "name": "Guava",
    "value": 2230000
  },
  {
    "name": "Lemon",
    "value": 4323000
  }
];