Ok, so I have completely stopped playing Skyrim (Legendary) due to having to delete my entire library of saves ( 2 level 50+ ) and the textures on NPCs and Dragons are purple, waaay too smooth, and even Alduin's fire attack is nothing but a bunch of flailing white polygonal white lines everywhere.

My disc is OK, but won't let me install to try and fix the problem, and yes, I do have enough space for an install.

I am going to go through and try and delete stuff to get past 10GB free space on my HDD to see if that helps the loading cache, at least it should from what I have read.

As you alluded to, this is most likely due to lack of free space on your HDD. Skyrim uses an excessive amount of memory to cache data, so hopefully the problem will clear up if your can have at least 10GB free.

I've had purple Dragons before too.

And purple Ragged Trousers as well.

I have over 10GB free, and did the whole clear Game Cache and not System Cache trick to no avail. FML

This is probably a dumb question, but have the settings on your display (TV or monitor) been changed recently or is there a cord loose somewhere? One time, the graphics went into weird colors when the cord from my Dell Monitor was not completely connected to my Xbox. Also, does this still happen if you were to start a new game or is it only on your existing games? Otherwise, I can't say that I can think of any other reason why this would be happening, unless something is going bad with your console.