Also, if you have photoshop or gimp then in one of the tabs at the top there is a button saying Threshold. Pressing that will turn it into pure black and white and you will be able to fill the line art in.

instead of saving the image from google or anywhere like this go to the actual site of the image and a download button should be somewhere on the page. This will make sure that the base will be pixelated and good to colour in. Deviantart is my fav website to find bases on so if you're not already on it you should give it a try.