Question

Ok, the idea is simple, set of buttons on the stage, click the button change to color to draw with. I’m trying to learn flash & actionscript and not really sure where my problem is, but I can not figure out how to do this.

package {
import flash.display.Sprite;
import flash.events.MouseEvent;

public class Artist extends Sprite {
    public var drawing:Boolean;
    public var colorArray:Array;
    public var dc;

    public function colors() {
        colorArray = ["0xFF0000","0xFFA500","0xFFFF00","0x00FF00","0x0000FF","0x4B0082","0x8F00FF","0xFF69B4","0x00CCFF","0x008000","0x8B4513"];

        for (var i:int = 0; i < colorArray.length; i++) {
        this["btn_" + i].addEventListener(MouseEvent.CLICK, set_color);
        }
    }

    public function set_color(e:MouseEvent):void {
        dc = colorArray;
    }

    public function Artist() {
        graphics.lineStyle(10,dc);
        drawing = false;
        stage.addEventListener(MouseEvent.MOUSE_DOWN, startDrawing);
        stage.addEventListener(MouseEvent.MOUSE_MOVE, draw);
        stage.addEventListener(MouseEvent.MOUSE_UP, stopDrawing);
    }

    public function startDrawing(event:MouseEvent):void {
        graphics.moveTo( mouseX, mouseY);
        drawing = true;
    }

    public function draw(event:MouseEvent) {
        if(drawing) {
            graphics.lineTo(mouseX,mouseY);
        }
    }

    public function stopDrawing(event:MouseEvent) {
        drawing = false;
    }
}

}

Answer 1

You should get the index by the button name, then you can assign the color using the clicked index.

for (var i:int = 0; i < colorArray.length; i++) {
    this["btn_" + i].addEventListener(MouseEvent.CLICK, set_color);
}

public function set_color(e:MouseEvent):void {
    // Get the button name and fetch it's index
    var index:int = int(e.currentTarget.name.substring(4));
    dc = colorArray[index];
}

Also, make sure the colorArray is known throughout the whole class if you want to access it in methods.
Just define it outside the colors method as Lukasz said:
protected var colorArray:Array and use numbers not strings for colors 0xFF0000 instead of "0xFF0000"