Links are turned purple only if your browser is allowed to keep memory of pages you visited.
You can change the number of days your browser is allowed to keep memory of pages you visited.
There must have been some recent change on your browser, cause there was no change on CureZone.
How to make changes on Internet Explorer:
You click on the Tools on the Main menu:
Tools > Internet Options
In the part that is called "Browsing history"
you click on "Settings" button.
A box appears called "Temporary Internet files and history settings"
Under "History" part it says:
Specify how many days Internet Explorer should save the list of websites you have visited.
Days to keep pages in history: 20
If you specify number 60, it will remember for you every single webpage you visited during the last 2 months, and every single link on CureZone you visited will turn purple.
If you specify number 2, it will only remember pages you visited during the last 2 days.