//Remove original arrows
//Use png at assets/selectArrow.png for the arrow on the right
//Set the background color to a BadAss Green color
background: url(assets/selectArrow.png) no-repeat right #BADA55;
…will get you started although you may need to be specific in your selector or use !important to override the browser default styling. Note also that this may cause other stylistic changes which you might not want.
Generally, if you want total control you use a different element/structure styled to look like a select….or even better a JS alternative.