Any tips on how to colour correct ND casts etc outside LR as part of the LRTimelapse workflow? There is not enough colour control in LR sometimes, especially bringing back blue skies. PS Batch action maybe as the first step?

No, you will have to use Lightroom, and it definitely works. It's not worth editing outside since you will lose your RAW files then and have to continue with jpgs, that makes it worse...

Try using White Balance, HSL, (Camera Calibration) - in that order.

Thanks Gunther, that's the order I have been using. I find it doesn't give the results obtainable with PS's selective colour etc in removing casts & bringing back accurate blue skies. A further colour tweak after rendering may help a little or a different ND filter...

I use the B+W filters, and have never had problems with those.