to T/S:
hi hi
i'm currently using a d300 and despite the numerous posts so far, i hope i can help with my own experience.
WB and lighting conditions : the d300 is actually a v v smart cam imo and most of the time, i can actually shoot with autoWB. however, if i don't want to shoot raw but still want to get accurate colours, i sometimes have to use the different preset WB settings (even outdoors in daylight, remembering that sunlight gets 'cooler' as the day progresses).
Exposure : i will have to agree with previous posters that shooting at ISO500 is a bit too much given the conditions u stated. rule of thumb for me: more details can be salvaged if i underexpose slightly (more so in raw, but works for jpg too) but nothing beats practice.
Colours : i noticed u mentioned u shot in Standard mode. Standard or Neutral modes on the d300 are recommended (see manual) for shooting in raw - where substantial pp will be done. if u search through the nikon discussions threads here, many have previously stated that the d300 out-of-camera colours are 'dull'. i initially found standard mode dull too and since then have downloaded the various picture controls to try. i believe you should try some of these too
Equipment : u have a winning combination for portraits d300 + 85/1.4. practise with both (and other lenses) loads and loads because mastering how to handle them (and their characteristics) will yield more 'keepers' (photos). frankly, i think the pics u posted show that u haven't shot enough with your combo, which explains why u are surprised that the pics turned out the way they did.
all the best for the future!