Can you post a picture? Does the invader grass ever get white seed heads? If so a picture of the seed head would be helpful.

Perennial rye doesn't just pop up in a lawn unless you live next to an unmowed field that contains PR. Most PR is dark green by the way, and blends well with KBG. Many sports fields are mixes of KBG and PR. I see where dchall is headed, could be poa annua. Pics of the offending grass would be very helpful (closeup pics).

tiemco, I do live next to a field but I don't know if there's any of this grass over there. I live downtown and most yards are pretty unmaintained so I'm usually dealing with a lot of weeds popping up in my parkway but I've never noticed this stuff until this year. I fee like it's PR because of the purple stalks. Here are some pics:

http://imageshack.us/photo/my-images/571/photo12qo.jpg/
http://imageshack.us/photo/my-images/585/photo22k.jpg/
http://imageshack.us/photo/my-images/864/photo32n.jpg/
http://imageshack.us/photo/my-images/854/photo41s.jpg/

*bump*

Hard to say, identifying grasses from pics is never easy, and yours aren't the best. There are plenty of websites that can help you with IDing grasses and weeds. Anyway here are the basics of the three cool season grasses (there are some other characteristics that aren't as obvious such as ligule shape and form, rolled or folded leaves in sheath, etc).

Tall fescue: Pointed tip, prominent veins, no obvious midrib. Edges are serated, but in turf types it isn't as prominent as in wild types.

Perennial rye: Fused speed boat tip, veins visible, dorsal midrib, front side dull, back side shiny.

KBG: Boat shaped (canoe) tip, no obvious veins, dorsal midrib, leafs are smooth and soft.

Poa triv and poa annua have the characteristics of KBG, but can be highly variable in appearance.