So you want to buy a screw... what kind of screw do you want to buy? Do you want to buy based upon the length? Or do you want to buy based upon the number of threads per inch? Or do you need a metric screw measured in threads per millimeter? Do you want to buy according to the number of independent helices ("single threaded" or "double threaded")? Or were you mostly interested in buying a screw to be used in wood, or metal, or rock, or plaster, or plastic? Or were you sent out to buy a Robertson's, a Phillips, a Square-Headed, or a Hex headed screw? A project you say -- so you mostly want to do fine finishing with recessed heads? This project involves outdoors -- are you mostly looking for a treated screw to use in pressurized wood, cause if you don't use a proper coating on those, you'll get metal creep something awful, not just surface rust but the screw will go completely spongy?
What's that? You want a left-handed screw?? Sorry, that there is a specialty screw; we don't carry those in this here corner store.
Moral of the Story: different color-spaces classify light in different ways that can be of more or less importance to some particular situation. RGB is like classifying screws according to intended material, thickness, and length (the typical primary scheme in stores around here): common and useful, but it does not directly address matters that might be important to you if you know (for example) that all you have handy is a Philips screwdriver and that you don't mind taking a hacksaw to the screw if it is too long.
The most common classification is not necessarily the best one for all purposes: RGB is good for mechanical display of colors, but HSV (for example) is much easier for humans to understand color relationships in. Some of the CIE color spaces are excellent for theoretical color computations based upon human physiology, but humans can find those spaces difficult to read.
