Hi Ken. Welcome to Nikonian's. Blue can be a problem with some sensors. I had problems with shooting flowers with either the D200 or D300 a few years ago. I see you have a D700. How does that work with blue clothing? Generally when you get a purple cast with dark clothing it can be caused by infra red contamination. If that is the case an inexpensive IR cut filter will eliminate it. This was a problem with the D2H and the Leica M8. Leica even furnished the filters free of charge. Sunlight is very rich in IR.
Have you tried other WB settings? Auto, Daylight and shade should work outdoors. I don't have a D3000 so I can't experiment with you. What 85mm lens do you have?
Here's a comparison shot of a black wind breaker shot with the D2Hs and an AI 85mm f1.8.
The 1st shot is without a filter.
This is the same scene but with a Tiffen Hot Mirror filter (IR cut). The jacket in this photo is the correct color.
The purple cast in the 1st photo is caused by IR. I don't have a blue jacket to photograph but I can see where blue could easily turn purple with this lighting if your camera has a weak IR filter on the sensor.
I only have the Tiffen Standard Hot Mirror filter but in a 52mm size for my manual focus lenses when I shoot UV photos. It filters the IR from the UV. It is a good filter and has been a standard for removing IR for years. The Tiffen T1 filter seems to do the same thing for a lower price.
I can't say that IR is your problem though. If you buy a filter you should be sure it can be returned if it doesn't work.
By the way synthetic fabrics like polyester will show the purple color shift much more than cotton.