This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
A workaround is to write a function to produce a window of your own font and color, name it 'alert()' (with proper parameters ofcourse) and make it available globally. In effect, it overrides the default alert dialog, and it worked well for me.