It turned out that my previous answer was not completely correct and I beg you to accept my apologies for this mistake.
In the Q3.2009 version of the control there is away to set up multicolor linear indicators (unfortunately not present in our online examples yet). The peak indicator can be created using a StateIndicator
Please, find the attached project which demonstrates how to set up RadGauge
for a similar scenario.
Hope this will help.
All the best,
the Telerik team