I've noticed that when you cut the part off the sprue. Instead use snips in reverse (flush side out) and snip the gate closer to the sprue than the part turning then after you have the part out and gate pieces still there turn snips around and flush cut against the part. I've noticed that when snipping the gates there is a small crystallization thing happening on the flush side of the cut which leads to having white-ish scaring at the point of separation. I've found that snipping in this fashion reduces the crystal effect and leaving less white marring to be removed or buffed out. Hope I explained this understandably. Thank you for the viewing. 
the crystallization you're talking about is from the plastic the kit is made from..
its really hard/brittle solid plastic, not the flexible-ish kind normal kits have, so when you snip it, instead of cutting the piece out, you end up cracking it off, causing the plastic to go white.
its pretty annoying building this kit lol, now that i finally got around to work on it.. it looks really nice, i gave up on "perfection", the sprues will almost always leave a mark, its just how the material is. Cutting it with a knife leaves less of a mark but the gate/sprue is really thick..... feels like im cutting some connector joints sometimes