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I don't recall such colourful diffraction spikes in Newtonians. At least not in images not using any form of lens (coma corrector, barlow, etc) before the camera.
Does a single or two edges produce the same effect as a diffraction grating? Also, the direction of the spectrum dispersion in a grating is also parallel to the direction of the lines, not perpendicular as seen in the OP's pic and in the Hubble pic.
My first thinking us the spectrum that is seen is also an artefact of internal reflections in the RC lens arrangement on because of the diffraction pattern. Further more because of the repeated sequence of the spectrum. The lens & coatings are not designed to deal with the diffraction caused by the spider.
Abberations have many different sources, and some are unexpected consequences, not all anticipated.
Alex.
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