Yes. Define a custom colour theme that matches the colours of your website. Make the border colour the same as your background colour. This is called "blending". Cryo.
Not that pays more so much as gets clicked more... You will have to use trial and error to discover what works best on your site. this will include changing color and placement/size of adds.
More importantly, the wrong colours can cause "Ad Blindness" in your visitors, hence the importance of "blending". Cryo.