Yes, best case scenario, you are losing a drive.  Amber/green indicates a "predicted failure".  This is most often a bad drive that has reported failing SMART information to the controller.  In some cases, this can signal a corrupt array - probable only if you did not delete and reconfigure a new array that had previously been in use before installing the OS.  Given the fact that you indicated having deleted the RAID 5 and created/initialized a new RAID 10, it is even more likely a failing drive.  You can run Online Diagnostics to confirm. You can access the manual directly here: support.dell.com/.../hom.pdf
Well, the support pages are down at the moment, otherwise I would have looked in the manual! So, I've got the above mentioned pe2900 with a perc5/i and 4x146Gb SAS 15k drives in a RAID10 setup.  After installing Hyper-V Server 2008r2sp1, one of them now has the above mentioned slowly blinking amber "health" light...blinks green, then amber, then off, and repeats. Am I losing a hard drive?  Other info: I deleted a RAID5 array, created the RAID10 array, and did a fast init. Then immediately rebooted to CD to install the OS. Not sure if I needed to do a full init first, but wanted to mention it. Thanks for any help with this!
Slowly blinking amber hard drive health light, poweredge 2900