Why is there color in infrared photos?

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Why is there color in infrared photos?
2 months ago

I shot this with an A3000 converted to infrared. It has a 750nm filter in place of the original hot filter. If you remove the lens, you see a black-looking rectangle where the sensor is.

I processed this in LR 5.6 using a custom camera profile to correct a lot of the raw white balance, and then used the WB dropper to correct more.

What I still don't understand entirely is where the color comes from. Pretty much all the light hitting the sensor was invisible infrared. I had always heard that the filters of the Bayer mask didn't block infrared at all, so that once infrared was allowed through to the mask, it would pass through all the elements fairly equally. Clearly that is not the case, but what is happening? Do the blue sensels pass more short IR, and the red ones more long IR? Or does that vary by sensor manufacturer? Or do the colors not even align in wavelength order?

I've Googled this quite a bit, but all the hits I've turned up were talking about IR in general and didn't discuss where these colors are coming from.

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A7 with kit lens and a number of legacy lenses (mostly Canon FD); A3000 converted to IR.

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Canon PowerShot G9 Nikon D200 A3000 Sony Alpha 7 Nikon AF-S DX Nikkor 35mm f/1.8G
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