Your comment about it not being supported is absolutely correct and I do not disagree. Your comment about using CSS variables is definitely a cool option, but unfortunately has very poor support right now. Your comment and reasoning as to _why _it will never be supported, however, is in my opinion wrong. One need only look at border and border-radius to see how it's entirely possible to accomplish this. Border accepts up to four entirely different sets of rules - one for each side - and yet it benefits from a plethora of different sub-rules and syntax to target specific sides or all sides together. I can either define all border colours at once with border-color, or I define just one with border-left-color. Same thing with border style, width, etc. Border radius works much the same way, with border-top-left-radius and the like. Having box-shadow-color and box-shadow-left-color makes sense and follows the standards set by other rules.

Your post is a bit more aggressive than it needs to be and fails to see other use-cases where defining just the colour is desirable. Hint: it has nothing to being lazy. For example, a website built on a template might have separate CSS files for the "master" layout styles vs. the "user" colour styles. The master file has all the base rules defined (border width, style, etc.) and is controlled by the developer while actual colours are in separate sheets and controlled by the designer(s). If a fix or change needs to be made to the layout, the developer can change it in one place without needing any of the designers to update their code. This is possible with border, background, and any other property that allows targeted rules but not box-shadow or text-shadow, which is unfortunate. This might not seem like a pain for one website, but when you have 30 different websites using the same master sheet it can become a nightmare to go through and manually update each of them. Again, this has nothing to do with being lazy and everything to do with scope, efficiency, access rights, and possibly more I'm not thinking of.