A bit rusty on pigments

I've just finished the first run at one of my Chimeras.  It's mostly finished, but there are thing I may go redo.  I went for a pale gray (fortress), same as the Valkyrie, but think I may have been better sticking with the darker gray of the sentinel (codex).  Also had a problem I've not noticed before, I need to seal after using pigments.  I rusted the model up some and then wanted to dry brush deneb stone to give it a dusty/dirty feel.  Well the rust pigment started turning it into Deneb Pink.  Note added:  Always do a quick sealer coat after pigments.  The rust itself was a bit of an issue too.  Managed to go way to heavy on one side, doesn't look too good.  Think I'll have to layer a bit of Fortress Gray over the top to tone it down some.  Lastly, the tracks.  They look amazing until I break out the sealer.  All I need to do is start shaking the can and they go all crappy.  I need to spend some time in Secret Weapon HQ, or bug Sirus over at GEG and see what they do to not have the can of sealer destroy your hopes and dreams decent looking weathering.