Links to wiki for reading:
Human eye color
Human hair color
Human skin color
Humans have a range of eye colors, but only one pigment, melanin, is present. A higher concentration causes a darker color. The remaining color variation comes from Rayleigh scattering. To get yellow eyes, you might need other pigments, that are not normally produced by humans.
Similarly, human hair color has only a few pigments, all melanins. There is some variation in the melanins, so we can get dark hair, blond hair, or reddish hair, but that is about it. Melanin can't make green hair to my knowledge. You might need other pigments to do that, which are not normally produced by humans.
Finally skin tones are mostly influenced by melanin (darker to lighter skin) as well, and also are affected by the color of the tissue beneath (the dermis, veins and arterioles, etc. will affect blueish and reddish tone)
So: Human coloration is limited for a specific reason: because we only produce certain pigments. If we take a look at birds for example, they produce other pigments we don't have to get striking colors:
So the question remains about how to obtain these pigments. You imagined mutations that produced other colors, but we have to consider what it mutation would produce such a color change, and why it would become distributed over the population. Additionally, different pigment families can produce different colors, so you will have to think about how this could have happened. If we stick with melanin your color range will be limited to brownish / yellowish / reddish colors for example. I have a feeling its not very likely for us to spontaneously gain the ability to synthesize carotenoids, for example, which color leaves, carrots, and salmon orange.
Thus mutation seems unlikely to give outlandish colors, if we are starting with modern human stock. Maybe a better solution is some sort of handwaving or genetic editing. Of course the question there is "what is considered natural".