• 背景画像の変更の仕方
  • http://jsfiddle.net/gh/get/jquery/1.7.2/highslide-software/highcharts.com/tree/master/samples/highcharts/chart/plotbackgroundimage/

plotBackgroundImageで画像を指定｡

var chart = new Highcharts.Chart({
 chart: {
 renderTo: 'container',
 type: 'line',
 plotBackgroundImage: 'http://www.highcharts.com/demo/gfx/skies.jpg'
 },

もしくは

• http://www.highcharts.com/demo/line-basic/skies

Highcharts.theme = {
 colors: ["#514F78", "#42A07B", "#9B5E4A", "#72727F", "#1F949A", "#82914E", "#86777F", "#42A07B"],
 chart: {
 className: 'skies',
 borderWidth: 0,
 plotShadow: true,
 plotBackgroundImage: '/demo/gfx/skies.jpg',

• 左の数字と下の月の消し方

http://jsfiddle.net/L9hNw/
xAxisとyAxisに以下のようにlabels.enabledの値をfalseにすると消えます｡

xAxis: {
categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'],
labels: {
enabled: false
}
},

• 線の色の変え方

http://jsfiddle.net/L9hNw/1/

chart = new Highcharts.Chart({
colors: [
'pink','red','green','purple'
], 

調べ方：
Highcharts API Reference
の左のｶﾃｺﾞﾘを適当に眺めればすぐ見つかりました｡

http://www.highcharts.com/demo/line-basic/skies