Sometimes, an abundance of color options is a hindrance. Analysis paralysis, amirite? To this end color.css reduces the number of stops in the expanded palette to three, save for yin (it only has two) and yang (it only has one).
If you want more granularity (read: opacity), you can call the raw version of the color (append -raw to the variable name) which will return the OKLCH values so you can do something like this: oklch(var(--uchu-light-gray-raw) / 40%).
var(--uchu-light-gray)var(--uchu-gray)var(--uchu-dark-gray)
var(--uchu-light-red)var(--uchu-red)var(--uchu-dark-red)
var(--uchu-light-pink)var(--uchu-pink)var(--uchu-dark-pink)
var(--uchu-light-purple)var(--uchu-purple)var(--uchu-dark-purple)
var(--uchu-light-blue)var(--uchu-blue)var(--uchu-dark-blue)
var(--uchu-light-green)var(--uchu-green)var(--uchu-dark-green)
var(--uchu-light-yellow)var(--uchu-yellow)var(--uchu-dark-yellow)
var(--uchu-light-orange)var(--uchu-orange)var(--uchu-dark-orange)
var(--uchu-light-yin)var(--uchu-yin)var(--uchu-yang)
If you know what Sass is, you'll know how to use color.scss. I didn't provide raw versions of them because Sass comes with so many color tools (and, I've been using regular CSS variables in my Sass anyways).
If you are a fan of CSS-in-JS or need to programmatically grab color values, there's color.json and color.ts includes available.