Aluminum pigtails from certain fixtures

Why do some fixtures come with what appears to be stranded aluminum? The instructions says it is to be used in copper installations (it's a leviton timing switch). The leads coming from the switch look like stranded aluminum, and I have seen this on some lighting fixtures as well. So my questions are:

1) Is this actually stranded aluminum?
2) What is the risk (if any) of connecting these leads to a copper pigtail?

thx

Could it be tinned copper that you are looking at?

It's highly unlikely that it is aluminum. As noted, it is probably tinned copper strands (which costs more and is less likely to corrode). If you cut them and look carefully at the end with a magnifying glass, you'll probably see copper colored metal in the middle.