Partial Mash: Is an Hour too long to steep?

So I just finished with my 3rd batch doing a partial mash.

I generally steep my grain for about an hour at around 155.

I honestly can't say that there has been anything wrong with the taste of my beer. The only thing I can say is that it is probably darker than normal.

So am I totally screwing everything up by doing it this long? Should I do more like 1/2 an hour? Pros/Cons to either way?

When you do a regular mash it is almost always an hour long, so steeping or partial mashing for an hour won't do anything but get you ready for all grain. Partial mashes should probably be done for about an hour anyway, steeping you can get by with 20-30 minutes, but an hour won't hurt.

I do mine for an hour. Conversion probably completes within 45, but it doesn't hurt to go a little longer. Most of the color influence from the grain seems to happen in the first 10-15 minutes, so I don't think going longer makes it any darker.

One thing that might help with color (if you're not already doing this) is adding the extract late in the boil instead of the beginning. I shoot for 3 gallons of runoff between the mash and sparge, add only add about a cup of extract at the beginning and then put the rest of the extract in at the 10 minute mark (off heat while adding). I've been able to make some pretty light colored brews this way.