RFR:8199893:the javadoc tool generates pages with a low constrast

[Priya Lakshmi Muthuswamy]

Hi,

Kindly review simple fix for 
https://bugs.openjdk.java.net/browse/JDK-8199893
webrev : http://cr.openjdk.java.net/~pmuthuswamy/8199893/webrev.00/
Thanks,
Priya