Do ND filters really ruin your footage?

Hello fellow camera geeks, people often say to me that ND filters (particularly variable ND filters) ruin the colour in your footage. But ND filters are an essential tool for filming video outdoors so that you can keep you aperture open and shutter speed at the correct 180 degree angle...hmm tricky!

And then there's the argument of sharpness, many say that buying an expensive lens that's really sharp and then screwing additional filters in front of it ruins the sharpness.

So is this true? Do ND filers ruin the colour and sharpness in your footage...? I HAD to find out! 

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