Not a pro at photography but have a background in medical imaging so take this with a pinch of salt. Before switching to the 10x lens, you're digitally zooming in, while maintaining the same matrix size/Resolution, there is therefore less signal to be binned into each pixel, reducing your Signal to Noise ratio. The increased noise in each pixel is impacting the colour represented in each pixel.
When actually taking a picture at 9.9x does the image still look different after post-processing?
