Our cold season grass (rye, fescue, blue grass) stays green in spring
and fall, but turns brown in the winter when the ground freezes solid
and there is snow on the ground. The only thing green then is the
dandelions and plantain and, by spring, the dead nettle is coming strong.

This is not my experience. The bluegrass in my lawn stay green through
out the winter. The differences in our experiences may be caused by:

1. I am in zone-6. May be you are in much colder region.

2. May be our definition of "green" is different. For me,
"off-green" is still green.

One more thing is that I am under the impression that "rye" is not as
cold tolerate as other cold season grass. If you have plenty of rye in
your lawn, they "may" die and turn brown in very cold weather.
Honestly, I am not exactly sure about this because I don't
intentionally seed rye in my lawn, and have very little experience
with rye.

Anyway, if your lawn turned brown in winter, the shredded brown leaves
probably can blend well on the lawn. And I can understand why you have
no problem leaving shredded leaves on the lawn.

Have a good weekend!

Jay Chan