CMYK is for subtractive color space (ink on paper) and RGB is for additive color space (your phone display). RAL, like Pantone CMS, is a color management system for enforcing consistency across different media and contexts (so that the plastic pigment on an item, the ink mixed for its package, and the colors used in its advertising all match). None of those examples can be used arbitrarily. They serve different purposes or are only applicable to specific, unrelated media.
Imperial and Metric entirely overlap, unlike your comment about color spaces and systems. In fact they overlap so thoroughly that the US stopped using standard Imperial weights and measures (which provide the definitive inch, pound, etc.) and simply define them in relation to their Metric counterparts. I snarked earlier about Americans simply using metric the hard way, but I don't think it's exactly wrong. A case can be made that there's a lot of money wasted each year because manufacturers have to come up with two sets of items (one for the US and Myanmar, one for the rest of the world) -- the principle of economies of scale say it's cheaper to simply make everything metric.