What is it about White Scars that tempts me so? I mean, I know I can't paint them as they have absolutely the most unforgiving colour scheme ever invented. Yet there's an attraction to the idea because they're very different from the (excuse the expression) standard template Space Marine army.
And they're absolutely one of my favourite ideas in Warhammer 40,000. They are superhuman, power armoured Mongolian horse archers except that since they're too large and heavy to ride a horse they ride giant motorbikes instead! They don't fortify positions or hold ground in any way, total freedom of movement is at the heart of how they prosecute their wars. I love to settle my games in combat, I find ranged fighting unsatisfying, so they're pretty much perfect for me.
They also don't make use of a load of things that have always been mainstays of my Space Marine armies. They don't operate Devastator Squads as they're far too static, using tanks Rhino-mounted Tactical Squads for fire support. They don't use Dreadnoughts (and I bloody love Dreadnoughts) because locking a White Scar inside a metal box, forever disconnected from the feeling of the wind on his face, is nothing short of a nightmare for them. They don't have Chaplains, merging the role with their Librarians.
Chris Wraight's excellent Horus Heresy novel Scars made me love this idea even more since it presented their philosophy of war in these terms: structures have weaknesses and will always fall once an enemy identifies the location of that weakness. Constant movement eliminates the existence of an identifiable centre, which the Khan views as the ultimate weakness. In fact, Wraight has the Khan pretty much predict the inevitability of something like the Horus Heresy simply because the Imperium has centred its massive beaurocracy on Terra.
There's also a lovely throwaway line in which Malcador the Sigilite (aka God's Best Mate) forgets the Khan when discussing the unaccounted-for Primarchs and muses “That was why he was created, after all.”. (He also has a line in which he reflects that he told the Emperor to make the Primarchs daughters instead of sons).
But.. painting white. I know I said I cracked it but that much white is a whole other challenge. Ugh...