Yesterday, I was just star gazing and I noticed some star-like object moving with a high speed somewhere near the Orion's Belt and exhibiting all the seven colors i.e VIBGYOR and after a few moments, it disappeared. Any plausible explanations for this observation?
Probably a satellite flare
It sounds like a satellite flare.
Coming, showing up clearly for a few moments, moving, then going away, are characteristic of a satellite flare, like Iridium flashes.
The changing colours can be explained with "Twinkling".