Xyz is an additive color space based on how the eye intereprets stimulus from light. Unlike other additive rgb like Rgb, Xyz is a purely mathmatical space and the primary components are "imaginary", meaning you can't create the represented color in the physical by shining any sort of lights representing x, y, and z. It's complicated to explain in a nutshell, so read more about it here:
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Color conversions performed using the open source ColorMine library.