Brown (burned) spots on white material

Recently I made my first Prusa i3 printer. It works great and is printing the objects exactly as I need them. However, during a build with white material, I will occasionally get brown spots on the build; most likely burned material. Sometimes it's small blobs (1-2mm) and sometimes it's larger blobs (5-7mm). I'm okay with it when it's just inside the build as support material, but it looks bad when it shows up on the outside of the build. Is there anyone else that has faced this problem, and if so; how can I fix this (I'm using Simplify3D btw). Thank you for any help you can offer.

Well you don't really supply any info about the machine, the material you use or your settings so a shot in the dark is that you may be printing too hot. Show some photos and give all ther pertinant info for a better guess.

Ive had this recently with some white abs.
It was material that had stuck to the extruder nozzle previously and got on to the nice white printed abs.

Clean the outside of your nozzle and the block once in a while.
I find some acetone on cloth when the nozzle is hot removes some of it while some needs scraping off.

Also remember any colour filament you have recently used is going to look quite dark against the white filament.
It may not be burnt material just remnants stuck on the hot end thats slowly worked down till it gets on your print.

Gordon

I had it happen once and found that my heater block was not tight enough letting filament leak out and bubbles which make little brown spots in the print, so just cleaned and tightened it up and all was well.