Yes it's varnish, and per OVERKILL's creation mechanism.
Varnish is polar, and likes to stick to metal surfaces. Oil is typically non polar, and has a limited ability to hold/carry varnish, holds more with higher temperature. In an engine, varnish is most likely formed in the ring belts, and in the blowby regions in the crank-case, then floats around waiting for some cooler surface to plate out on.
The thing is, it will build up in the oil, and nothing happens until it's carrying capacity is reached, then it bombs out, and every gramme made after that plates out.
Typically harmless (althour in my turbine life, the cool spot is governors and valve actuators, and if they stick, kaboom...)
Had very similar on my L67 Caprice. Photobucket playing up, so can't post pictures yet.
Tried AutoRx, some other crazy stuff, and went back to first principals with 1,000 mile oil changes on a 15W40 that was advertised as having great cleaning...all did nothing.
If you want to test what I'm saying, take one of your valve covers, and use hot water and clothes washing powder...they are polar, very polar, and strip the red stuff right off...not really applicable to the rest 'though.
Just keep up regular OCIs with a good oil, and don't worry too much about it.