One thing that always bothered me is that the RGB values aren't perfect multiples of 8. Why? That makes it a lot cleaner to look at for one, lol. That's what I personally do for my colors in RGB.
Another thing to note is, the whole background and sprite layer limitations things; it's really not necessary to pull off the 16-bit aesthetic. Same with NES or GBC styles; just following the four colors per sprite/tile rule (with one transparent where necessary) gets you the 8-bit style. Following the other arbitrary limitations doesn't add anything of value to the style. And animation doesn't need any limitations at all; you can have an 8-bit style with smooth animations, as seen with many true 8-bit titles. Just take your time and polish everything to the maximum under the color limitations per sprite/tile only, and you'll be fine.
Another thing to note is, the whole background and sprite layer limitations things; it's really not necessary to pull off the 16-bit aesthetic. Same with NES or GBC styles; just following the four colors per sprite/tile rule (with one transparent where necessary) gets you the 8-bit style. Following the other arbitrary limitations doesn't add anything of value to the style. And animation doesn't need any limitations at all; you can have an 8-bit style with smooth animations, as seen with many true 8-bit titles. Just take your time and polish everything to the maximum under the color limitations per sprite/tile only, and you'll be fine.