In Minecraft I was in a server and I saw a swamp with green and purple grass. and the trees were purple with the vines. I know it isn't Myselium because that only uses Mushrooms to use that block. and I planted Mycelium on the ground and put a tree next to it but that didn't work. How do I make it look like a swampy theme for my house in Creative on flat land with only some water and What tree Someone tell me please!
Many colors of grass and trees come from biomes. Swamp biomes have darker, purple-y grass than plains, forests, etc. Likewise, the color of the trees' leaves come from this biome color data. If the grass isn't as purple as mycelium this is probably what you're seeing.
Unfortunately, this means that once in a biome, any grass is forced to that color, regardless of where the grass came from. This means that you can't dig up "swamp grass" and plant it in a forest or a jungle — it will just change color.
Sometimes the borders between biomes change rapidly and result in trees with different color halves and grass of different color seemingly in the same biome. This may be what you're seeing in your swamp.
Here is a jungle with a swatch of swamp on its border, showing the above effect: