Is it always white in the same exact spot, and no changes in size?
Does that spot swell also or stay the same when the swelling happens?
can you or anyone feel any kind of pulse or warmth on that spot compared to other parts of the same vein?

Depending on the answers to those questions ...or they may not apply at all..
If it usually stays the same most of the time I guess I would wonder if it might be plaque build up..