Message font / background colour

HI, is it possible to change the colour of the text / background when messages are shown. In this example, i have created an account and the message reads:
'Your account has been created and an activation link has been sent to the e-mail address you entered. Note that you must activate the account by clicking on the activation link when you get the e-mail before you can login.
Upon clicking on the activation link, your account will be activated and you will be able to continue your order'

However, because of the colour of the website, the text is not visible. I would preferably have no background and just white font if possible.