I noticed my oil on my rb25 stays gold for about 3,500km roughly. Then goes light brown after that. Probably around 4,500 mark it goes dark brown (this is me driving normally with no / minimal pulls as i blow black smoke when i boost) (when I drain the oil it's black at 5,000 no metal shavings though in the filter or oil)
I noticed now that it's been under 3,000km and it's dark brown. I think it's because I've been doing a few pulls more than usual (pulls means, in first gear going up to 5000-7000 rpm)
My oil doesn't smell like fuel at all, and isn't causing me any issues but I don't want to get bearing wear (yes I'll be getting my car tuned soon to)
I don't know if it's just me or if my oil is a bit thinner (I'm comparing brand new oil to oil that has roughly 2,500km from memory so might not be a good comparision.