Pitching on the cake - dark to light

I am brewing a porter right now (it is in primary), could I pitch a pale ale onto the cake or is it bad to go from dark to light?

I've always heard that it's a bad idea. You could wash it and get better results

I've done it with no ill effects. Either try and siphon as much liquid as possible out of the carboy (tilt). If it still looks a bit dark; toss some water in there; like a 1/2g swirl it around, let it sit 15m and siphon that out.

If you've never threw a batch onto a yeast cake, the next batch isn't going to be in there long. Maybe 36hr at the most. Blowoff is highly likely.

I just saved the yeast off of my Fat Ass Tired. I had a near boil over, and a good hot break. So my trub finally was two colored, dark below (hops?) and a whiter layer above. I swirled the left over beer that I had left in the carboy gently and it seemed to dissolve the yeast pretty good, leaving the hops sludge. Then I poured the liquid into a beer bottle and capped it. I think I got more yeast and less flavor than I usually do. This will be the 4th time I use this yeast. Originally Cal V liquid. Flat assed tired, Brown Rye, Flat Assed tired, probably F.A.T. again next time. I do make a starter when I use the bottled stuff. Not if I have a frsh batch starting, then I pour the yeast from one carboy to the next, leaving most of the trub behind.

Since one cup of sludge is adequite for re-pitching, I think trying to swirl the yeast off the top of the hops, and using only 8-12 oz in a 640oz batch won't transfer much of the dark flavors to a light batch.