Is my turtle sick?

Question
Hi there...
I have two turtles, I was given them, so I'm not sure exactly what kind they are but I think they are Macquarie turtles?  Anyway, I went to feed them tonight and noticed that the big one (he's about 20cm long) has gone a funny colour on his shell.  The very top of it (where it peaks) is the same dark olive colour it's always been, but the rest of it has gone really pale.  It's not soft, slimy or furry, just a strange colour.  I'm a bit worried about him, but I don't want to take him to a vet if it's a normal thing that happens. Thanks heaps for the help.
Libby.

Answer
1. Identification: Knowing the species will help a lot. you can find the identity by
- looking at the World of Turtles gallery at http://www.austinsturtlepage.com
- sending me a photo link
- going ot the identification forum at http://www.turtleforum.com

If it IS a Macquarie, it might be better known as the Murray River Turtle from Australia.

2. This may be a form of shell rot. I am not very familiar with the Australian turtles, so the best I can suggest is to try the forums at http://www.turtleforum.com

Sorry!