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In my experience, the Bayer matrix in a colour QHY5L-II doesn't affect guiding with a guidescope to any real extent, as long as you have a fairly low f ratio. It's plausible that guiding on a red star might make the centroid jump about through a Bayer matrix, but as long as the guide star covers more than around 10 pixels on the sensor it's fine. I've ran a numerical simulation to see how the centroid would move about with a Bayer matix, and it's really not very much even on red stars.
With a OAG (and high f ratios) guiding is likely to be more difficult with a colour webcam. You're losing around one third of the light with a Bayer matrix and you tend to need as much light as possible with OAG at high f ratios in order to get a guide star. My guidescopes operate at around f/5 so that a colour webcam is fine. Dropping down to guiding at f/8 I would need a mono webcam to get the same number of guidestars, since 8x8 / (5x5) is roughly equal to the factor of three you gain with mono vs colour.
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