Because I have a lot of projects which require a lot of colors, I went down the rabbit hole of building a factory to obtain every type of dye, terracotta, wool and tinted glass. I had fun making it but I wish I made concept art before hand. There is no clear central point when looking at the factory.
To make a rainbow factory, you first have to locate a flower forest. It is the only biome which grows a wide variety of flowers which (almost) can be processed into every color. I built a train so I can get to the flower forest fairly fast. I know elytras exist but this is more fun.
Because we are getting a large portion of the colors from flowers, there needs to be a hyper-efficient way of collecting these flowers. I built a high-efficiency bonemeal factory to feed the harvester which collects the flowers.
Once the harvester is loaded with bonemeal, it traverses across the entire flower biome and picks up as many flowers as possible. The flowers then get crushed into dyes and turned into different mixtures of colors and blocks. Then they're put into storage for players to come by and grab.
For black, green, and brown, there is a tree farm, a cactus farm, and a cocoa bean farm. The output of those farms are processed into dye. For wool, sheep are tortured for eternity and sheared for their coat.
While the factory serves its purpose, it could be better. Because it is inconvienient for players to go all the way to the factory to get stuff, I was thinking of making it so a train stops by and takes the factory output to a player hotspot. The factory could be faster and some design choices could be improved. Lastly, the way it looks is detailed, but I do not know where to put my eyes when I look at it. Its such a mix of random colors and features, it does not know what it wants to be.
