Which dyes can be easily mass-produced in Minecraft?

I'm making some pixel art on a map. I can easily make automated wool farms to get as much wool as I need in all 16 colors. Colored terracotta, on the other hand, cannot be mass-produced. I can get some colors from mesa biomes, but the majority need to be manually dyed. Which dyes can be mass-produced, i.e. automated to the extent that I can get many stacks with only a few minutes of manual labor?

• White can be mass-produced by making a skeleton grinder or automatic composter to produce bonemeal. Making a skeleton grinder will take more than just a few minutes, but it's required for most other colors, so it is worth the investment.
• Green can be mass-produced by a cactus farm.
• Yellow, magenta, red, and pink can be easily obtained by using a dispenser to bonemeal sunflowers, lilacs, rose bushes, and peonies, respectively.
• Blue can be automated with a cornflower farm like so.
• Light gray can be automated in a similar fashion using other flowers.
• Lime, orange, light blue, cyan, and purple can be obtained by combining the colors above.
• Brown, as mentioned in SF's comment below, can be mostly automated. "Cocoa grows when bonemealed with dispenser and drops when the wood it's attached to is moved." The only manual part is planting the cocoa beans, though that can be automated in several ways, e.g. by putting a paperweight on your mouse button.
• Black is more difficult to automate, and may not be worth the effort. The two main methods are a wither rose farm and a squid farm, both of which take time to do correctly.
• Gray can only be obtained by combining black and white, so you need one of the black dye farms mentioned above.